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HANDBOOK

A COLLECTION OF THE

MINERALS OF THE BRITISH ISLANDS,

MOSTLY SELECTED FROM THE

LUDLAM COLLECTION,

IN THE

MUSEUM OF PEACTICAL GEOLOGY,

JERMYN STREET, LONDON, S.W.

F. W. RUDLEE, I.S.O., F.G.S.,

LATE CURATOR OF THE MUSEUM.

LONDON :

PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE,

BY WYMAN & SONS, LIMITED, FETTER LANE, E.C.

And to be purchased from
E STANFORD, 12, 13, and H, Long Acre, London ;
JOHN MENZIES & Co., Rose Street, Edinburgh ;
HODGES FIGGlS & Co., Grafton Street, Dublin;
From anv A^ent for the sale of Ordnance Survey Maps ; or through any
Bookseller from the Ordnance Survey Office, Southampton.

nos.

Price One Shilling.

GENERAL MEMOIRS.

SUMMARY OF PROGRESS of the GEOLOGICAL SURVEY for 1897, 1898, 1899, 1900, 1901, and 1902. Each Is.

PLIOCENE DEPOSITS of BRITAIN. By C. Reid. 5s. Bd.

CRETACEOUS ROCKS OF BRITAIN.— Vol. I. GAULT AND UPPER GREENSAND OF ENGLAND. 9s. Vol. II.

LOWER AND MIDDLE CHALK. 10s. Vol. III. UPPER CHALK. 10s. By A. J. Jokes-Browne and W. Hill.
JURASSIC ROCKS OF BRITAIN.— Vol. I. YORKSHIRE, 8s. 6d. Vol. II. YORKSHIRE, Fossils, 12s. By

C. FOX-Strangways. Vol. III. LIAS OF ENGLAND (Yorkshire excepted). 7s. Bd. By H. B. WOODWARD.

Vol. IV. The Lower Oolitic Rocks of England. 10s. By H. B. Woodward. Vol. V. The Middle and Upper

Oolitic Rocks of England. 7s. Bd. By H. B. Woodward.
BRITISH ORGANIC REMAINS. Decades I. to XIII., with 10 Plates each. Price is. Bd. each 4toj 2s. Bd. each 8ra.
MONOGRAPH I. On the Genus PTERYGOTUS. By T. H. Huxley and J. W. Salter. 7s.
MONOGRAPH II. On the Structure of the BELEMNITIDjE. By T. H. Huxley. 2s. Bd.

MONOGRAPH III. CROCODILIAN REMAINS found in the ELGIN SANDSTONES. By T. H. HUXLEY. 14s. 6d.
MONOGRAPH IV. On the CHIMjEROID FISHES of the British Cretaceous Rocks. By E. T. Newton. 5s.
VERTEBRATA of the PLIOCENE DEPOSITS of BRITAIN. By E. T. Newton, 4s.

Museum Catalogues, &e. :—

HANDBOOK to the MUSEUM of PRACTICAL GEOLOGY. Bd.

FOSSILS .-—CAMBRIAN and SILURIAN, 2s. Bd. ; CRETACEOUS, 2s. 9d.; TERTIARY and POST-TERTIARY Is. &?.

DISTRICT MEMOIRS.

MEMOIRS of the GEOLOGICAL SURVEY OF GREAT BRITAIN. Vol. I. ESSAYS by DE la Beche and Others.

21s. Vol. II. Part 1, MALVERN HILLS. By J. PHILLIPS. 21s. Part 2, ESSAYS. 21s. Vol. III. N. WALES.

By Sir A. C. Ramsay. App., by J. W. Salter ana R. Etheridge. 2nd Ed. 21s.
CAMBRIDGE. By W. H. Penning! and A. J. Jukes-Browne. 4s. Bd.

CORNWALL, DEVON, AND WEST SOMERSET. INDEX to De LA Beciie'S Report on. By C. Reid. Is.
DERBYSHIRE, NORTH. By A. H. GKEEN, (C. LE Neve Foster and J. R. Dakyns. 2nd Ed. By A. H Green

and A. Strahan. 5s. Bd.
FENLAND. By S. B. J. SKERTCHLY. 36s. Bd.
HOLDERNESS. By C. REID. 4s.
ISLE OF MAN. By G. W. Lamplugh. 12s.
ECONOMIC GEOLOGY OF ISLE OF MAN. Is. 6d.

TERTIARY FLUVIO-MARINE FORMATION of the ISLE OF WIGHT. By Edward Forbes. 5s.
ISLE OF WIGHT. By H. W. Bristow. New Ed. By C. Reid and A. Strahan. 8s. Bd.
ISLE OF PURBECK AND WEYMOUTH. By A. Strahan. 10s. id.
LAKE DISTRICT, NORTHERN PART OF. By J. C. Ward. 9s.

LANCASHIRE, SUPERFICIAL DEPOSITS OF SOUTH WEST. By C. E. DE RANCE. 10s. Bd.
LONDON AND PART OF THE THAMES VALLEY. By W. Whitaker. Vol. I., 6s. Vol. II., 5s
MIDLAND COUNTIES, TRIASSIC and PERMIAN ROCKS of the. By E. Hull. 5s.
NORFOLK and SUFFOLK, VERTEBRATA of the FOREST RED SERIES of. By E. T. Newtox. 7s. Bd.
NORWICH. By H. B. Woodward. 7s.
RUTLAND, &c. By J. W. Judd. 12s. Bd.

WEALD, (Parts of KENT, SURREY, SUSSEX, and HANTS). By W. TOPLEY. 17s. Bd.
Eruptive Rocks : —

ERUPTIVE ROCKS of BRENT TOR. By F. Rutley. 15s. ed.
FELSITIC LAVAS of ENGLAND and WALES. By F. Rutley. 9<f.

Iron Ores of Great Britain : —

Part II. South Staffordshire. Price Is. Part III. South Wales. Price Is. 3d. Part IV. The Shropshire Coal-
field and North Staffordshire. Is. 3d.

Coal Fields: —

BURNLEY COALFIELD. By E. Hull, R. H. Tiddeman [and Others], 12s.

YORKSHIRE COALFIELD. By A. H. Green, R. Russell [and Others]. 42s.

EA8T SOMERSET and BRISTOL COALFIELDS. By H. B. Woodward. 18s.

WARWICKSHIRE COALFIELD. By H. H. Howell. Is. Bd.

CHEADLE COALFIELD. By G. BARROW. 2s.

LEICESTERSHIRE COALFIELD. By Edward Hull. 3s.

SOUTH WALES. (See under Sheet Memoirs, New Series).

Sanitation and Water- Supply : —

SOILS AND SUBSOILS from a SANITARY POINT of VIEW. By H. B. Woodward. 2s. Bd.

WATER SUPPLY OF SUSSEX. By W. Whitaker and C. Reid. 3s.

WATER SUPPLY OF BERKSHIRE, By J. H. Blake and W. Whitaker. 3s.

Gun Mints: —

MANUFACTURE OF GUN FLINTS. By S. B. J. Skertchly. 16s.

SHEET MEMOIRS OF OLD SERIES MAPS.

London Sheet. Guide to the GEOLOGY of LONDON and NEIGHBOURHOOD. By W. Whitaker. 6th Ed is
4 - - FOLKESTONE and RYE. By F. Drew. Is.

34 - - PARTS of WILTS, and GLOUCESTERSHIRE. By A. C. RAMSAY, W. T. ATELINE, and E. Hull 8rf

44 - - - CHELTENHAM. By E. HULL. 2s. Bd.

45 - - BANBURY, WOODSTOCK, and BUCKINGHAM. By A. H. Green. 2s.
45 SW -WOODSTOCK. By E.HULL. Is.

47 - • • N.W. ESSEX & N.E. HERTS. By W. Whitaker, W. H. PENNING, W. H. DALTON, & F J Bennett i„ «,?

48 SW - COLCHESTER. By W. H. DALTON. Is. Bd. ' ■ ° a -
48 SE - EASTERN END of ESSEX (WALTON NAZE and HARWICH). By W. Whitaker Bd

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49 S, 50 SE - ALDBOROUGH, &c. By W. H. DALTON. Edited, with additions, by W. Whitaker. Is
49 N - - SOUTHWOLD, By W. WHITAKER. 2s. ed.

PREFACE.

The Museum of Practical Geology has long possessed
collections of British rocks and British fossils arranged with
special reference to their mode of occurrence in the field; but
until recently it has not possessed a general collection of
British Minerals arranged on the same basis, although the
materials for making such a collection were present in the
Museum, mainly in the valuable series of specimens bequeathed
by Mr. Henry Ludlam.

On the retirement of Mr. Rudler from the post of Curator, I
was fortunately able to retain his services for the special purpose
of arranging a collection on the lines above referred to. He has
now completed the work, and upwards of 1,700 specimens have
been duly arranged, labelled, and placed on view in the
Museum.

Although the present Handbook has been prepared primarily
as a guide to the collection, I am confident that it will be found
to possess a permanent value quite apart from the specimens to
which it relates. Whilst it is sufficiently explanatory to form a
treatise which will prove of interest even to those who are
unversed in mineralogy, it is detailed enough to be serviceable
to scientific students, especially to students of geology and
mining. The copious footnotes, with references to the original
authorities consulted in the preparation of the work, are of great
value and afford evidence of the thoroughness with which the
subject has been dealt with.

I cannot allow the present opportunity to pass without placing
on record my high appreciation of the services rendered to this
Institution by Mr. Budler during his long tenure of office as
Curator, and of the great skill and knowledge which he has
displayed in arranging the collection of British Minerals and in
writing this Handbook.

J. J. H. Teall,

Director.

Museum of Practical Geology,

Jermyn Street, London.

December 2\st, 1904.

7**2. 2,500— Wt. 965. 1/05. Wy. & S. 2426r.

CONTENTS.

Introduction

CASE I.— DIVISION 1.

Minerals of Cornwall and Devon.

Cassiterite and its associates

Cassiterite
Stannite

CASE I.— DIVISION 2.

Minerals of Cornwall and Devon— Continual
Minerals associated with Cassiterite .

Paok

15
20

yuartz .

Apatite .

Topaz .

Fluorite

Fluellite

Lithia-Mica .

Gilbertite

Tourmaline .

. 28

Axinite

Wolframite

Scheelite

Mispickel

CASE II.— DIVISION 1.

Minerals of Cornwall and Devon

— Continued.

Copper Sulphides and Snip ko-f err ites

. 33

Chalcopyrite .

. 35

Chalcocite

. 37

Covellite ....

. 38

Erubescite

. 39

CASE II— DIVISION 2.

Minerals of Cornwall and Devon

— Continued.

Copper-bearing Minerals of the Gozza

ns . . .40

Cuprite ....

Melaconite .

. 43

Native Copper . . . .

. 44

Malachite and Chessylite

. 45

Chrysocolla . . . . .

. 46

Chalcanthite

. 46

Langite, Woodwardite, etc. .

Connellite

Atacamite, etc.

. 49

VI CONTENTS

CASE III.— DIVISION 1.

Minerals of Cornwall and Devon — Continued. page

Arsenates and Phosphates from the Copper-GozzoMS . 50

Olivenite, Libethenite, etc. ... .51

Clinoclase and Cornwallite . 52

Liroconite ..... 52

Chalcophyllite • 53

Bayldonite, etc. . 53

Andrewsite, Chalcosiderite, etc. . . 53

CASE III.— DIVISION 2.

Minerals of Cornwall and Devon — Continued.

Ores of Lead, Zinc, Antimony, etc. .... 54

Galena, Cerussite, and Pyrornorphite . . 55
Silver Ores . .56
Zinc Ores . 58

Antimony Ores 59

CASE IV.— DIVISION 1.

Minerals of Cornwall and Devon — Continued.
Sulphides and Sulpho-Salts
Pyrite

Mispickel

Bournonite .

Tetrahedrite and Tennantite

Vivianite
Ludlamite, etc.
Childrenite .
Pharmacosiderite
Scorodite, etc.
Cronstedtite .

02
02
04

CASE IV— DIVISION 2.

Minerals of Cornwall and Devon— Continued

Ores of Iron, etc . 65

Magnetite . . 65

Hsematite . . . . 67

Gbthite and Limonite . 68
Chalybite

69
70
71
71
72
73
73

CASE V— DIVISION 1.

Minerals of Cornwall and Devon— Continued.

Minerals of the Rarer M 'eh ds .... 75

Nickel and Cobalt Minerals . ... 75

Manganese Minerals . . . 70

CONTENTS. vii

CASE V. -DIVISION 1— Continued.

-Minerals of Cornwall and Devon— Continued. PA0E

Manganite, etc. . ... 77

Dialogite, etc. . 77

Bismuth Minerals . ... 78

Pitchblende . . 79

Uranite . 81

Churchite . . . 83

CASE V.— DIVISION 2.

Minerals of Cornwall and Devon — Continued.

I he hpara of the Mineral Veins

Fluorite

CASE VI.— DIVISION 1.

Minerals of Cornwall ad Devon — Continued.

The Spars — Continued

. 90

Quartz ....

Calcite . . . .

Dolomite

Barytes . . . .

. 94

CASE VI.— DIVISION 2.

Minerals of Cornwall and Devon — Continued.
Miscellaneous Minerals 95

Chalcedony .
Calcite

Wavellite

. 98

Felspars, etc.

Garnets, etc. . . . .

99
. 100

Serpentine, etc.

Allophane, etc.

Pigotite

Retinite ...

102
. 103
. 104
. 104

CASE VII.— DIVISION I.

Minerals of Somersetshire, Wales, etc.

Minerals of West Somersetshire .

. 105

Minerals of the Mendips . . . . .

. 107

Lead Ores . . . . .

. 107

Mendipite . .
Zinc Ores

. 107
. 109

Iron Ores ' .

. 110

Potato-stones

. Hi

Vlll

CONTENTS.

CASE VII— DIVISION 1— Continued.

Minerals of Somersetshire, Wales, etc. — Continued.

Minerals of the Bristol District. page

Iron Ores, etc. . 112

Celestite . . 113

Minerals of the Forest of Dean 116

Minerals of South Wales 117

Millerite . . .120

Hatchettine . . . 121

Minerals of Mid Wales . . .121

Minerals of North Wales . 123

Lead and Zinc Ores, etc 123

Manganese Ores . . 125

Copper Ores . . J 26

Anglesite .... .127

Brookite, etc. . . 128

Gold ... . .129

CASE VII. -DIVISION 2.
Minerals of Derbyshire.

The Spars, etc.

131

Calcite

132

Elaterite .

134

Fluorite .

135

Barytes . . . .

135

Quartz

136

CASE VIII.— DIVISION 1.

Minerals of Derbyshire— Continued.

The Ores

. 137

Galena

. 137

Cerussite

. 138

Anglesite, etc. .....

139

Matlockite and Phosgenite or Cromfordite

139

Zinc Blende

140

Calamine, etc. ......

. 141

Minerals from Ecton .....

142

CASE VIII— DIVISION 2.

Minerals of W. Cumberland and N. Lancashire.

Haematite Deposits ... ... 143

Haematite, etc .144

Quartz ...... 148

Calcite, etc 149

Aragonite . . . . 149

Barytes, etc 151

CASE IX.— DIVISION 1.

Minerals of Cumberland. page

Minerals of the Caldbeck Fells and the Lake District 152
Apatite .... .153

Wolfram and Scheelite . . . 153

Molybdenite ... 154

Grunlingite . . . . . 154

Pyromorphite, etc. ... . 155

Cerussite, Anglesite, and Linarite . . . 157

Malachite, Brochantite, etc. . . . 157

Hemimorphite . 158

Tourmaline, Garnet, etc. ..... 159

Graphite . . 159

CASE IX.— DIVISION 2.

Minerals of the Northern Lead Districts.

Ores of Lend and Zinc, Barytes, etc.

16]

Galena . ...

162

Cerussite . . ...

165

Zinc Blende :

165

Calamine, ej;c

166

Chalybite, Pyrite, etc.

167

Barytes

168

CASE X— DIVISION 1.

Minerals of the Northern Lead Districts — Continued.

Spars, other than Heavy Spar.

Witherite

Bromlite and Barytocalcite
Calcite and Aragonite

CASE X— DIVISION 2.

Minerals of the Northern Lead Districts -

The Spars — Continued

Fluorite
Quartz

Minerals of Shropshire .

Minerals of Leicestershire .

CASE XL— DIVISION 1.

Minerals of the Neozoic Strata.

Chiefly from the Midlands and S.E. England .
Halite, or Rock-salt

Gypsum

Anhydrite . ....

Celestite .......

170
171
172

■Continued.

174

. 174

176
177
178

180

181
182
185
186

X CONTENTS.

CASE XL— DIVISION 1— Continued.

Minerals of the Neozoic Strata — Continued. page

Barytes . 186

Copper Ores, etc. . 189

Iron Ores . .191

Glaueonite 195

Pyrite 196

Marcasite 198

Quartz 199

Allophane . . 200

Aluininite or Websterite 201

Calcite . . 201

Jet and Amber . . 202

Copaline, etc. . . . 203

CASE XI.— DIVISION 2.
Minerals of Scotland.

Minerals of the Leadhills District . 205

Minerals of Strontian . . . 210

CASE XII.— DIVISION 1.

Minerals of Scotland — Continued.

Minerals of the Midland Valley . . . 213

Minerals of the Highlands . . 219

Minerals of the Western Isles, etc. . .221

CASE XII.— DIVISION 2.
Minerals of Ireland.

Minerals of Leinster . . 222

Minerals of Gonnaught . . . 226

Minerals of Ulster ... .227

Minerals of Munster . . 231

Minerals of the Isle of Man . . 232

Index 235

A HANDBOOK

To A

COLLECTION OF BRITISH MINERALS.

INTRODUCTION.

Ever since the foundation of the Museum of Practical Geology,
a collection of the metal-bearing minerals of the British Islands has
formed an important feature in this institution. In this Collection
the ores of each metal have been grouped together so that a visitor
interested, for example, in the mining of copper-ores, or in the
industrial applications of copper, finds all the copper-ores of the
country represented in one compact section. The advantages of
this simple arrangement have been frequently acknowledged by
students of mining and metallurgy. With regard, however, to those
minerals which do not contain the common or heavy metals, and
which are therefore sometimes loosely termed '" non-metallic," no
attempt had, until recently, been made to separate the British from
the foreign specimens. Yet the separation seemed for many reasons
desirable. In an institution intended primarily to illustrate the
geologv of the British Islands there should undoubtedly be ex-
hibited a collection, as complete as possible, of the mineral pro-
ductions of the country. Such a collection, though very far from
complete, has been recently formed ; and this collection it is the
purpose of the present Handbook to describe.

The Museum of Practical Geology has long possessed, through its
relation with the Geological Survey, an unrivalled collection of
British rocks ; it also possesses a stratigraphical collection of British
Fossils, which, in certain respects, is without parallel elsewhere ;
and now, by the addition of a special collection of British Minerals,
supplementing the fine mineralogical collections already exhibited,
the institution has become a fairly faithful exponent of all depart-
ments of science bearing on British Geology.

The collection of British minerals, numbering about 1,700 speci-
mens, is installed in a series of twelve double table-cases, placed on the
Principal Floor of the museum. The restriction of the collection
within these limits is due rather to the want of additional space
than to any lack of material. By far the greater number of the

7X8-2. B

- INTRODUCTION.

specimens here exhibited have been selected from the valuable
cabinets bequeathed to the institution by Henry Ludlam, Esq.; but,
where necessary, the Ludlam minerals have been supplemented by
specimens selected from other departments of the museum. Yet
the impoverishment of the general collections has been but slight,
and the fine series of British Ores, which has always been a special
feature in the museum, is still practically intact.* It may be noted
that the specimens in this older series are mostly of large size, many
being massive examples of ore admirably fitted for display in a public
museum, whereas the specimens in the new collection, having been
derived mainly from a private cabinet, are comparatively small in
size.

In arranging this newly-formed collection of local minerals, it has
not been considered expedient to follow any of the ordinary systems
of classification, based on chemical composition. On the contrary, it
has been felt that the wants of the student of geology, and to a less
extent those of many students of mining, might be best met by an
arrangement which is fundamentally topographical. No doubt a
local arrrangement leads to some unavoidable overlap, similar
minerals occurring in different localities ; but this inconvenience is
amply compensated in other ways. By bringing together all the
minerals of a particular region, so as to illustrate their natural
association, some light may be thrown upon the conditions of their
formation. After all, it is the origin of minerals that is philosophic-
ally the fundamental feature of interest about them. The specimens
have consequently been selected not so much for their perfection of
crystallisation — though this, of course, has not been overlooked — as
with a special view of illustrating their paragenetic relations and
their mode of occurrence in the rocks.

Sowerby, writing as far back as 1811, remarked that " the various
circumstances which attend a mineral are very convenient to be
known. "f It is these attendant circumstances that have received
special attention in selecting the specimens to form this British
collection, and in preparing this Handbook.

Although the mode of occurrence of the several minerals and their
geological relations have been specially insisted on in this work, it
has yet been deemed desirable that the economic aspect of mineralogy
should not be altogether neglected. Brief reference has conse-
quently been made, wherever possible, to the industrial applications
of the minerals of the British Islands.

It should be explained that this Handbook has been prepared
with a two-fold object. Primarily it is intended for the use of
visitors, who, without any special acquaintance with mineralogy,

* The specimens which do not belong to the Ludlam collection are indicated
by a red disc on each of their labels.

+ "British Mineralogy." By James Sowerby. London: 1811, vol. iv.,
p. 174.

IXTKODUCTION'. 3

may desire to learn something about the Collection of British
Minerals. Experience has shown that an intelligent visitor on
seeing a specimen is apt to ask about it these questions : 1. What
is it ? 2. Where doej it come from ? :3. How has it been formed ?
4. \\ hat is its use. ? \n endeavour is consequently made in this
guide-book to give simple answers to such enquiries.

In order that the work may be self-interpreting, most of the
technical terms, which are necessarily used in the description of
minerals, receive brief explanation. It has not, however, been
considered necessary to explain ordinary chemical expressions,
since these are now generally understood. In endeavouring to
answer questions relating to the origin of minerals, much difficulty
is encountered ; for in the present state of our knowledge, not-
withstanding all that has been written, it rarely happens that a
mineralogist can speak with certainty as to the way in which a
given mineral has been formed. Still, an attempt has been made
in these pages — though generally but a brief and vague attempt —
to meet, if not to satisfy, enquiry on this subject ; and this has led
to the occasional introduction of matter of a rather speculative
character.

^ hilst this Handbook is thus intended to serve the purpose of
the ordinary visitor to the Museum, it is believed that it may also
prove serviceable to many students of geology and of mining. It is
principally for their use that copious references to original authori-
ties have been introduced, in the shape of foot-notes. Such refer-
ences would be useless, not to say pedantic, in a popular guide-book,
but they become invaluable in a work likely to be used by serious
students.

In the preparation of this Handbook the ordinary sources of
mineralogical information have been consulted, but special acknow-
ledgment should be made of the elegant volume of Professor Miers,*
the classical work of the Danas,f and the elaborate treatise of Dr.
Hintze.J For British mineralogy the standard work of Greg and
Lettsom^ has naturally been used with freedom. In that work,
written nearly half a century ago, the number of mineral species
occurring in the British Islands is given as 241. Since that time
many others have been added, and a Supplementary List was

* " Mineralogy, an Introduction to the Scientific Study of Minerals." By
Henry A. Miers, D.Sc, M.A., F.R.S. 1902.

■f " The System of Mineralogy of James Dwight Dana : Descriptive
Mineralogy." 6 ed. By Edward Salisbury Dana. Xew York. 1896.

% " Handbuch der Mineralogie." von Dr. Carl Hintze. Leipzig. {In
Progress. )

§ " Manual of the Mineralogy of Great Britain and Ireland." By Robert
Philips Greg, F.G.S., and William G. Lettsom. London. 1858.

It may be mentioned here that several papers on " The Mineral Topography
of Great Britain " were contributed by A. W. Tooke, M.A., F.G.S., to the
Mining Review, commencing in 1836.

~K*2. B 2

4 INTRODUCTION.

contributed by Mr. L. J. Spencer to the British Association in
1898.* According to this authority the number of species known
in Great Britain and Ireland at that date was 293. It must not be
supposed, however, that representatives of all these species are to
be found in this Collection.

In closing this introductory chapter, the writer is anxious to
acknowledge the assistance which he has received in the preparation
of this work from his former colleagues of the Geological Survey
and Museum— especially from Mr. Horace B. Woodward, F.R.S.,
Mr. Clement Reid, F.R.S., and Mr. Aubrey Strahan, F.R.S.

* " Supplementary List of British Minerals." By L. J. Spencer, M.A ,
P.G.S. Beport of British Association, Bristol meeting, 1898, p. 875. Abo,
Geological Magazine, New Series, Dec. 4. Vol. vi. (1899) p. 75.

MINERALS OF CORNWALL AND DEVON.

CASE I.

DIVISION 1.
THE MINERALS OF CORNWALL AND DEVON.

Cassiterite and its Associates.
(Nos. lfoOS.)

In a topographical arrangement of a collection of British minerals
it seems desirable, for several reasons, to start with the south-
western peninsula. No part of Britain of equal extent has yielded a
greater number or a richer variety of minerals, whilst the extensive
mining operation!! carried on for so long a period in this area have
afforded exceptional facilities for studying- the natural conditions
under which the minerals occur.*

It has not been considered desirable to separate the minerals of
Cornwall from those of Devon. The River Tamar, though forming
for the most part a convenient dividing line between two
counties, can in no sense be regarded as marking a geological
boundary. East Cornwall and West Devon are united by structural
homogeneity. Indeed, all Cornwall and though not all Devon-
shire, at least that part which includes Dartmoor and the country
to the west may be regarded as forming a single geological area.

In a catalogue of Cornish minerals contributed many years ago to
the Royal Geological Society of Cornwall.f by the late Mr. John
Garby, an enthusiastic local collector, something like 150 species and
varieties were enumerated as occurring in Cornwall. But even this
number was much increased by Mr. J. H. Collins, when he published
in 1871, his " Handbook to the Mineralogy of Cornwall and Devon." +

* Becher, an. old German mineralogist, writing at Truro in the seventeenth
century, says (or rather, is made to say by his translator), " The earth is here
so abundant in different kind of fossils that I believe there is no place in the
world which excels Cornwall in the quantity and variety of them ; and I con-
fess I have found here a mining-school." Quoted in " Observations relative
to the Mirjeralogical and Chemical History of the Fossils of Cornwall." By
Martin Henry Klaproth. Translated by John Gottlieb Groschke. London,
1787, p. ii. The term " fossil," used in this quotation and in the title was
formerly employed in its wide sense to include minerals as well as organic
remains, and, in fact, literally anything " dug up."

f " A Catalogue of Minerals found in Cornwall, with their Localities." By
John Garby, Esq., Trans. Hoi/. Oeol. Soc. Cornwall, vol. vii. (1865) p. 72.

} A Handbook to the Mineralogy of Cornwall and Devon." By J. H.
Collins, F.G.S. Truro and London, 1871.

So far as Devonshire is concerned, the late Mr. Townshend M. Hall con-
tributed a paper " On the Mineral Localities of Devonshire " to the Devonshire
Association in 1868. See Trans. Dev. Assoc, vol. ii., Part ii. (1868) p. 332 ; and
addenda in vol. iii. (1869), p. 76. The late Mr. F. Rutley gave a list of rrine-
rals from the neighbourhood of Tavistock in the Geological Suivey Memoir
on Brent Tor (1878) p. 50-

G MINERALS OF CORNWALL AND DEVON.

Although the south-western peninsula has thus yielded so great a
diversity of minerals, and these frequently of such beauty as to
justify its description as " the natural mineral cabinet of Britain,
it ' must not be supposed that fine specimens, such as are here
exhibited, are now to be readily obtained from this part of the
country. Not only is the mining industry of Cornwall and Devon
much less active than formerly, but the older mines now working are
not prolific in cabinet specimens of crystallised minerals. It was
observed by the late Mr. W. Jory Henwood, a distinguished authority
on the mines and minerals of Cornwall, that crystals are far more
numerous near the surface than at great depths. * It is in the
shallow workings, within range of meteoric influences, that we
naturally expect to find most of those beautiful oxides, carbonates,
phosphates, arsenates and other oxidised products for which old
Cornish collections are celebrated. The collection here exhibited is
particularly rich in fine examples of such minerals. Many of the
important specimens in the Ludlam collection were obtained from
the famous Turner collection formed by Heuland in the early years
of the last century ;f whilst others were purchased, thirty or forty
years ago, from the late Mr. Richard Tailing, an intelligent collector
of Cornish minerals, at Lostwithiel. At the present time it is practi-
cally impossible to procure such specimens, except from old collec-
tions.

Most of the minerals of Cornwall and Devon here exhibited have
been obtained from mineral-veins, or lodes. The crystals are
frequently found studding the walls of cavities in the veinstone, such
cavities being known as vugs or voughs. The veins are irregular
sheet-like masses of mineral matter, varying in length, in thickness
or width, and in depth. Usually they are highly inclined, and in
some cases stand in a position nearly vertical. % Whilst some veins
consist of mineral matter which has been deposited in pre-existing

* "" Observations on the Metalliferous Deposits of Cornwall." By W. Jory
Henwood, F.R.S. " Reprinted with alterations and additions " from Journ.
Roy. Inst. Cornwall, vol. iv., No. xiii. (1872), p. 8 of renrint. Also Trans. Boy.
Cteol. Soc. Cora., vol. v. (1843\ p. 206.

f These minerals are described in Levy's catalogue : " Description d'une
collection de Mineraux, formee par M. Henri Heuland, ct appartenant a
M. C'h. Hampden Turner." Par A. Levy, 3 vols, and Atlas. London : 1837.
In this work the localities of the British specimens are often given very vaguely
and the Cornish minerals are generally referred simply to " Cornouailles."
Such lack of definite location is not, however, restricted to these specimens.
When minerals are purchased from local dealers there is often not unnaturally
some reticence with regard to the exact mine, or other source, from which a
specimen may have been obtained. Probably, the dealer himself does not
know precisely, since it is to the interest of a person who finds the mineral to
guard his own knowledge of the locality with some jealousy. Many of the old
Cornish specimens were obtained surreptitiously by the miners, and it was a
matter of importance to them that the discovery should not come to the
knowledge of the captain of the mine, or of any of the adventurers. To the
geologist this want of exact information as to locality is a serious loss.

\ The inclination to a vertical plane is called the hade or underlie of the
lode, and that to a horizontal plane the dip.

TIN-ORES. 7

fissures in the rocks, others appear to be bands, or sheets, of altered
rock, impregnated with certain metal-bearing minerals. Many of
the Cornish tin-lodes belong to the latter class, as pointed out by
the late Sir Clement Le Neve Foster.* The rock in the immediate
neighbourhood of the lode is known to miners as the "country?' In
Cornwall and Devon it usually consists either of granite, or of the
slaty rocks termed killas. or of some of the igneous rocks, like quartz-
porphyry, that pass under the general name of el van. t

The course, or strike, of the lodes which carry tin and copper-ores
in the West of England, though varying considerably in different
districts, may be said to be generally north of east and south of west.
Their direction is, therefore, roughly parallel to the general trend of
the south-western peninsula ; nor does it differ greatly from that of
the series of large granitic bosses which stretch from Dartmoor to
the Land's End. In addition to these tin and copper-lodes, there
is a later set of veins, or cross-courses, r unni ng roughly in a north
and south direction, and frequently carrying ores of lead and
zinc (p. 54).*

The minerals of Cornwall and Devon occupy the whole of Cases I
to VI in this collection. Each case consists of two parts, recognised
as Divisions 1 and 2. Case I. is devoted to the exhibition of a series
of specimens, illustrating the characters of Cassiteritp, the common
ore of tin, its associated minerals, and its mode of occurrence.

Native Tin. or tin occurring naturally in a metallic state, though
not unknown, is a substance of extreme rarity. Even when it has
been recorded, doubt has not unfrequently been raised as to its
authenticity ; and specimens from Cornwall, regarded formerly as
native tin, are now generally believed to be nothing more than
smelted products from ancient workings, known locally as " Jews'-
house tin.";;

Tin is found in nature almost invariably as an oxide. It is true
that it is known also as a sulphide, which, in association with copper
and iron sulphides, forms the mineral termed stannite (No. 68, p. 20),
but this is a substance quite local and exceptional in its occurrence.
Practically all our tin-ore is tin oxide. This mineral — the native

* For a modern description of lodes consult " A text-book of Ore and Stone
Mining." By C. Le Neve Foster, B.A., D.Sc , F.R.S., 3rd ed., 1900, p. 7, : also
'■■ A Treatise on Ore Deposits." By J. Arthur Phillips, F.R.S., 2nd. ed. by
Henry Louis, M.A., 1896. See also Sir Archibald Geikie's " Text-book of
Geology," 4 ed., 1903, p. 807.

f The geology of Cornwall is described in the earliest of the memoirs of the
Geological Survey. " Report on the Geology of Cornwall, Devon and West
Somerset." By Henry T. De la Beche, F.R.S., etc. 1839.

% The Trans. Bay. Owl. Soc. Cornwall may be referred to for numerous
papers on the mineral veins by Mr. W. J. Henwood, Sir W. W. Smyth, Sir V.
Le Neve Foster, Mr. J. H. Collins, Mr. J. B. Hill, Mr. Donald MacAlister and
others.

§ On ancient ingots of tin and on the old smelting works called Jews'
Houses see Mr. Henwood's paper in Jmirn, Bey. Inst. Corn., vol. iv. (1873.)
p. 240.

8 MINERALS OF CORNWALL AND DEVON.

dioxide, or stannic oxide, Sn 0,— is known to the mineralogist as
Cassiterite and to the miner as tinstone, or simply " tin.''*

Although tin can hardly be described as a rare metal, its ores are
rather restricted in geographical distribution. Cornwall is one of
the oldest and best known, and geologically one of the most typical,
tin-bearing countries of the world.

The remarkable discovery that copper, a comparatively soft
metal, could be rendered fit for the production of cutting instru-
ments with a hard and keen edge, by the addition of about ten
per cent, of tin led to the early recognition of the exceptional
value of the white metal. For the production of this alloy Cornwall
supplied tin to some of the early centres of civilisation in the
Mediterranean, probably as far back as the so-called Bronze Age.
It has sometimes been supposed that this part of the world was
known as the " Cassiterides," or " Tin Islands " — a view supported
recently by M. Salomon Reinach.f

At the present day, after having supplied tin for perhaps thirty
centuries, Cornwall remains the most important tin-producing centre
in Europe : indeed, with the single exception of " the Straits," it
stands at the head of all the tin countries of the world. j According
to the official statistics issued by the Home Office, the amount of
dressed tin-ore obtained in Cornwall during the year 1902 was 7,552
tons, 3 cwts. valued at £5 13, 303. § It is notable that of this amount
as much as 1,828 tons, or nearly one-quarter of the total output, came
from the single mine of Dolcoath — a mine which is at once the
deepest and the most productive in the county. The lodes worked
at this mine were originally in killas and yielded copper-ore, but

* Although it is not deemed necessary in this Handbook to enter into details
with regard to the origin and meaning of mineral names, it seems desirable
to point out with regard to tin-stone, perhaps the most interesting and
characteristic of all British minerals, that the mineralogical name is taken from
Kurrairepoc; ( Kassiteros), the Greek word for tin. Some philologists have held
that the connection of this word with the Sanskrit kaslira suggests that the
earliest tin must have been brought to Europe from the East, perhaps from
Khorassan or from the famous tin-producing localities of Malacca and Banca.
Kecently, however, it has been suggested that Kacro'iTtpoi; may have been de-
rived from a Keltic source. (M. d'Arbois de Jubainville, Les Celtes.)

The old Cornish word for tin was stean. According to Beckmann the word
slannum came to be definitely applied to tin in the fourth century. The
stannum of Pliny was a pewter-like alloy, whilst tin was known to some Roman
writers xi plumbum album or white lead. Metallic tin is still known in this
country as white, tin, to distinguish it from b/arlc tin, which is the term applied
to the dressed ore.

f The reader will find the classical references to Britain conveniently
collected and translated in the folio work : Monument Historica Britonnica.
1K48. For information on prehistoric bronze, see Sir John Evans's " Ancient
Bronze Implements " (London, 1881) and the British Museum " Guide to the
Antiquities of the Bronze Age " (1904). In discussing the source of tin for
early bronze-making, the occurrence of tin-ores in Tuscany must not be
overlooked.

+ Kothwell's "Mineral Industry.'" Vol. xi. (1903). p. 586.

§ "Mines and Quarries: General Report and Statistics for 1902 " Edited
byC. T.e Neve Poster, D.S'c, F.R.S. (1903), p. 276.

TIN'-ORES. \)

passing downwards they entered granite, and then, as often observed
elsewhere in the West of England, the copper gradually gave way to
tin.

Observations in many parts of the world have shown that there
exists between the occurrence of tin-ore and the presence of granite,
cr rocks of similar type, so constant a relationship as to suggest a
causal connection. Whether in Cornwall or in Saxony and
Bohemia, in France or in Spain, in the Malay Peninsula or in New
South Wales, not to mention other localities, the occurrence of
cassiterite seems to have been determined by the intrusion of an acid
magma. Moreover in all these localities the cassiterite is associated
with a peculiar group of minerals characterised by the presence of
fluorine, and — in a less marked degree — boron, phosphorus and
arsenic.

As far back as 1*41 M. Daubree, struck with this relationship, sug-
gested that the tin had been brought up from plutonic sources in the
form of a volatile fluoride.* This seems to have been the first
occasion on which attention was directed to the function of fluorine
as an important mineralising agent whereby the metal could be
carried from deep-seated sources into mineral-veins.")" Daubree's
views were taken up by Elie de Beaumont in his lectures at the
College de France, and elaborated in his famous paper on volcanic
and metalliferous exhalations.*

Subsequently Daubree carried out his classical experiments on the
artificial production of cassiterite by the reaction of water- vapour
on tin fluoride, or rather chloride.^ This synthesis conclusively
demonstrated the possibility of what had previously been only a
feasible conjecture as to the manner in which oxide of tin might
have been formed in nature. As a matter of convenience Daubree
used the chloride instead of the fluoride; but the halogens, chlorine
and fluorine, are so closely related as mineralising agents that the
substitution was perfectly allowable. It is clear, however, that in
the natural formation of tinstone fluorine was the prime agent, since
in nearly all cases, there are certain fluorine-bearing minerals which
form a group of satellites around the tin-ore.

Although Daubree has the merit of having been the first to suggest
the relation of fluorine to the genesis of tin-stone, the influence of

* " Memoire sur le gisement, la constitution ct 1'origine des amas de minerai
d'etain." Annates des Mines, 3e serie, tome xx. (1841) p. 65. A committee
of reference, reporting on a paper presented to the Academy of Sciences -in
1841, said : " M. Daubree est le premier, qui ait donne au fluor une puissance
pour ainsi dire creatrice." Comples Rendus, tome xiii. (1841), p. 834.

+ The term " mineralising agents," or mineralisers, is given, following the
French school, to those bodies which render others volatile, or promote

Qiologiqu

Recherches sur la production artificielle de quelques especes minerales
cristallines, particulierement de l'oxyde d'etain, de l'oxyde de titane et du
quartz." Annates des Mines, 4e serie, tome xvi. (1849), p. 29. See also
Daubree's ' Etudes synthetiques de Geologie experimentale," 1879, p. 37.

10 MINERALS OF CORNWALL AND DEVON.

this element as a subterranean agent in the alteration of felspar-bear-
ing rocks had been recognised as early as 1824 by Leopold von Bucn.
In order to account for the formation of certain deposits of kaolin
near Halle, this geologist invoked the aid of hydrofluoric acid, and
supported his suggestion by pointing to the abundance of fluor spar
in the decomposed rock.* In like manner fluor spar and other
fluorine-bearing minerals occur in the altered granite in Cornwall,
suggesting that here also fluorine may have been responsible for the
alteration. This view is supported by Mr. J. H. Collins, who, in
describing the Hensbarrow granite, refers to the constant presence
of minerals containing fluorine in the china-clay districts."}" Mr.
Clement Reid's study of the granites of Western Cornwall led him to
conclude that the masses of china-stone, or kaolinised rock, which
have very local distribution superficially but great downward
extension, may represent pipes up which fluoric and boracic vapours
escaped. + It seems, therefore, probable that in certain cases,
perhaps in many, kaolinisation may have proceeded from below
upwards, and that the agent of alteration may have been some com-
pound of fluorine, either in solution or as a solfataric exhalation.
Such alteration of granite at one locality obviously does not preclude
other means of alteration elsewhere ; and the commonly accepted
view, based on the researches of Forchhammer and of Bischof , that
kaolin has been formed by the alteration of felspar through the action
of meteoric waters containing carbonic acid, still admits of local
application.

With regard to the stanniferous deposits in Cornwall it may be
pointed out that Dr. Richard Pearce, now of Denver, suggested as
far back as 1864 that many of the Cornish tin-lodes, so far from being
mineral deposits in definite fissures, were simply masses of altered
granite, more or less impregnated with tin-ore. § This view has been
ably developed by Sir C. Le Keve Foster, who has shown that such
important ore-deposits as the Great Flat Lode, near Carn Brea, are
of this nature. || The greater part of this lode is an ill-defined band
of tin-bearing schorl -rock, adjacent to a thin quartzose vein, called
the leader, which represents a narrow fissure filled with brecciated
veinstone. This crack, or joint, may have served as a channel for
the ascent of vapours or solutions, which acting on the neighbouring
rock, whether granite or killas, might effect its alteration, with de-
velopment of schorl and deposition of cassiterite.

* Min. Tascht'/nJxich, 1824, p. 437. Gesammelte Schriften, vol. iii. (1877),
p. 186.

t " The Hensbarrow Granite District." By J. H. Collins, F.G.S., Truro :
1878, p. 36.

j '•'' Summary of Progress of Geological Survey for 1901 " (1902), p. 26.

S " The Influence of Lodes on Rocks." Rep. Miners' Assoc. Cornwall.
Truro : 1864, p. 18.

|| " On the Great Flat Lode south of Redruth and Camborne, and on some
other tin deposits formed by the alteration of Granite." By C. I* Neve
Foster, B.A., D.Sc., F.G.S. Qvart. Journ. Geol. Soc, vol. xxxiv. (1878),
p. 640.

TIN -ORES. 11

The band of altered rock immediately adjacent to the vein is
usually called in Cornwall a rape!, but there is a gradual transi-
tion between the lode and the capel on the one hand, and on the
other between the capel and the unaltered " country."*

Similar alteration of granite, with formation of tin-lodes, was
described by Sir C. Le Neve Foster as occurring at East Wheal Lovell
and at some other Cornish localities. f At Cligga Head, near St.
Agnes, the granite in the vicinity of the tin-bearing quartz veins has
been converted into greisen — a granular quartz-mica rock, usually
carrying topaz — which is commonly associated with the tin-deposits
of Saxony. The formation of greisen at Cligga Head has been re-
cently studied in detail by Mr. J. B. Scrivenor.J who shows that the
felspar of the granite has been partly converted into muscovite,
quartz and topaz, and the biotite into brown tourmaline, magnetite
and quartz. In the centre of each band of greisen is a quartz vein
representing the narrow fissure from which the alteration proceeded,
and containing cassiterite, wolfram, mispickel, copper pyrites and
blue tourmaline : it is, in fact, a miniature tin- and copper-
lode.

It seems well established that the occurrence of tin ore in Corn-
wall, as in most other countries, is connected (1) with the presence
of an acid eruptive rock, (2) with the profound alteration of this rock,
and (3) with the association of a peculiar assemblage of minerals,
suggesting the nature of the medium by which the alteration may
have been effected. The precise details of the processes whereby
the ore has been formed and introduced into the veins, are still,
however, not free from obscurity.

Most of the Cornish lodes yield ores of both tin and copper ; and
i t appears that these heavy metals must have been derived originally
f rom the acid magma. Probably the tin was carried off in association
with fluorine, and the copper with sulphur. The vapour extracted
from the eruptive magma, j udging from the minerals occurring in the
lodes, must have contained such elements as fluorine, boron, phos-
phorous, arsenic and sulphur. While the emanations were at a
temperature above their "critical point,"§and therefore in avaporous
condition, they would produce in the rocks through which they rose
that kind of alteration termed pneumatohjtic. This action has been
carefully studied by Prof. J. H. L. Vogt, of Christiania, who in
recent years has devoted much attention to the genesis of

* On capels consult Mr. J. H. Collins's paper " On some Cornish Tin-stones
andTin-capels." Min. May., vol. iv. (1880), pp. 1, 103 ; vol. v. (1884), p. 121.

t " Remarks upon the tin-deposits of East Wheal Lovell." Trans. Roy.
Geol. Soc. Cornwall, vol. ix., part ii. (1876), p. 167 ; and " Remarks on some
Tin Lodes in the St Agnes District." Ibid., vol. ix., part iii. (1876), p. 205.

% " The Granite and Greisen of Cligga Head (Western Cornwall)." By
John Brooke Scrivenor, M. A., F.G.S. Quirt. Journ. Geol. Soc, vol. lix. (1903),
p. 142.

§ The critical point is that temperature above which the given substance
remains permanently gaseous, whatever the pressure.

■12 MINERALS OF CORNWALL AND DEVON.

ore-depoiits, and who is led to believe that the formation of
the tin-lodes probably commenced before the complete cooling of
the granite.*

In the tin-bearing districts of the Erzgebirge, or " Ore mountains,"
between Saxony and Bohemia, where the Cornish conditions are
closely paralleled, the alteration of the granite and the impregnation
of the ro.cks with tin-ore have been repeatedly studied by eminent
geologists and mining engineers. According to Dr. Karl Dalmer,
one of the latest and highest authorities, the Zwitter of Altenberg —
which is an altered granite containing tinstone — has resulted from
changes which took place after its solidification, but probably while
the deeper part of the granite was still in a glowing condition, so that
the vapours which affected the upper portion may have arisen from
the lower part even before complete consolidation of the magma. f

Although the formation of the tinstone in Cornwall and Devon
may have been initiated during an early phase of the granitic intru-
sion, while the plutonic mass if not molten was yet at a temperature
so elevated as to throw off highly heated vapours, it appears likely
that the deposition of the ore in its present position was effected,
partly at least, by the agency of thermal waters. Much of the tin-
ore, as we now see it, may be regarded as a deposit from solution
rather than as a direct product of the action of vapours.

The action of heated solutions, associated with fumarolic action,
has been described by Prof. Vogt a,:, pneumoto-hydoto-genetic. If the
tin left the magma as a volatile fluoride under great pressure, the
emanations escaping through the rocks would yield soluble matter
to the water, which must have been encountered as soon as the
physical conditions permitted liquidity. The tin, released from its
haloid combination by the action of water, whether vaporous or
liquid, would take the form of an oxide, which might be carried away
in solution, and ultimately form a deposit in cracks or an impregna-
tion in a rock, in either case constituting, if sufficiently abundant,
an ore-body.

It is true that tin dioxide is so sparingly soluble in water that
it is not unfrequently regarded as a substance practically insoluble.
It was found, however, long ago by Bischof J that cassiterite is
soluble in water charged with alkaline carbonates — salts which are
very common in natural waters. More recently C. Doelter has shown

* For Prof. Vogt's important work the following papers may be consulted . —
" Ueber die durch pneumatclytische Processe pn Granit gebunden Mineral-
Neubildangen." Zeitschrift fiir praktische Geolo /ie, Dee. 1894, p. 458,
" Beitrage zur genetisehen Classification der durch magmatische Diflerentia-
tionsprocesse und dor durch Pneumatolyse entstanden Erzvorkommen."
Ibid. April, 1895, p. 145. " Problems in the Geology of Ore-deposits."
Trans. American Institute Mining Enqineers, vol. xxxi. (1902), p. 125.

j "' Erlauterungen zur geologischen Specialkarte des Konigreichs Sachsen.
Section Altenbcrg-Z;n:nv.,l;l." Siwet 119. Leipzig: 1890, p. 66. Also:
" Der Altenberg-Graupener Zinnerzlagerstattendistrict." Zeitsch. f. prakl.
Oeologie, Aug. 1894, p. 313.

J " Lehrbuch der chemischen und physikalischen Geologie " 2nd Ed ,
vol. iii. (1866), p. 811.

TIN-ORE*. 13

that it is slightly soluble even in distilled water at 80°C, whilst the
solubility is increased by the presence of sodium fluoride, though not
by sodium chloride.* Its occurrence in the waters of certain hot
springs is inferred from its presence in deposits of siliceous sinter.
Thus, M. Errington de la Croix obtained from a warm spring at Ajer
Panas, in Selangor, a deposit consisting mainly of opaline silica like
geyserite, which was found, on analysis by Prof. Stanislas Meunier,
to contain • 5 per cent, of stannic oxide.f Here, then, is an example
of the contemporaneous formation of a tin-bearing deposit.

According to Mr. J. H. Collins, the antlers of the red deer, formerly
found rather abundantly in the tin- bearing gravels worked in the
Carnon and Pentuan valleys, were partially mineralised with cassit-
erite. His analysis of a specimen in the museum of the Royal
Geological Society of Cornwall showed the presence of 2-6 per
cent, of stannic oxide. J Mr. R. Q. Crouch, describing a certain
specimen, says " the whole horn had undergone a change into tin
ore."§ But possibly this may not imply solution of the tinstone.

In certain Cornish mines there have occasionally been found con-
glomerates and breccias, consisting of fragments of rock broken
from the walls of the lode and rolled pebbles washed into the fissure
cemented together with cassiterite and other minerals, which have
probably been deposited from circulating waters. No. 49 is a speci-
men of the famous conglomerate from the Relistian mine, in Gwinear,
described nearly a century ago by Mr. Joseph Carne,|| in which
cassiterite, in a crystallised condition, forms part of the cementing
medium. In a brecciated lode occurring at New Rosewarne mine,
and described by Sir C. Le Neve Foster, the agglutinating minerals
included quartz, cassiterite, mispickel, chlorite and pearl-spar.

Pseudomorphs — or those minerals which by chemical or mech-
anical alteration assume the crystal forms of other species, so that
their substance and structure bear no necessary relation to external-
form — are in many cases highly suggestive in discussing the origin
of minerals. Nos. 47 and 4* are examples of the well-known pseudo-
morphs of cassiterite after felspar from Wheal Coates,^! an old tin

* Journ. Chew. Hoc, vol. lviii (1890), p. 1070. Min. Slit., Bd. xi (1890),
p. 325.

f "' Examen chimique d'eaux minerales provenant de Malaisie ; minerai
d'etain de formation actuelle." Comptes Itendus (27th May, 1890), tome ex.,
p. 1083.

\ " Note on the occurrence of stanniferous Deerhorns in the tin-gravels of
Cornwall." Trans. Roy. Oeol. Soc. Corn., vol. x. (1887), p. 98.

§ " Notice of the occurrence of the Horns and Bones of several species of
Deer in the Tin Works of Cornwall." By Richard Q. Crouch, Esq. Trans.
Roy. Oeol. Soc. Corn., vol. vii. (1865), p. 185.

'! " An account of the Relistian .Mine." Phil. Trans., vol. for 1807, p. 293.

\ The word Wheal, denoting a mine, is the usual form in which the old
Cornish word Hud is now written. The late Mr. Robert Hunt tried in vain
to revive the original form. Writing in 1884 he says: "I have constantly
employed, since 1847, the lerm 'Huel ' which is undoubtedly the ancient
Cornish term — signifying a mine or mineral work — but the corruption ' Wheal '
is so undeviatingly used by all, that there is no reason why I should any
longer endeavour to bring the older term into use again." — " British Mining."
By Robert Hunt, F.R.S. '1884), p. 190.

1 4 MINERALS OF CORNWALL AND DEVON.

mine near St. Agnes, where they occurred at one time in great
abundance. The crystals present mostly the characteristic form of
Carlsbad twins of orthoclase* ; but while the shape has been faith-
fully preserved the felspathic matter itself has disappeared. The
replacing material consists largely of cassiterite, usually a granular
mixture of cassiterite and quartz. The lode which yielded these
remarkable pseudomorphs, which are said to have " occurred in
millions," was in a soft decomposed granite, or perhaps an elvan, and
contained so much sandy matter that it has been called a " sand
lode."f Similar pseudomorphs have been found, though but rarely,
at other localities in Cornwall, as at Cam Brea and at Balleswidden,
near St. Just. It seems probable that they were formed by the
pneumatolytic alteration of a porphyritic rock, after its consolida-
tion but while still in a heated condition. On the other
hand, it was contended by Bischof that ordinary carbonated waters,
coursing through tin-bearing rocks, might be competent to dissolve
felspar and to deposit tinstone in its place.

The presence of tin has been recorded in certain rock -forming
minerals, notably in zinnwaldite, a lithia-mica, where it probably
exists as microscopic inclusions of cassiterite. It has even been
suggested that in some silicates tin may partially replace silicon, that
tin dioxide may play the part of silicon dioxide. It was the presence
of the heavy metals in many rock-forming silicates that led the late
Prof. F. Sandberger to his well known views on the origin of mineral
veins by a process of lateral secretion.\ According to this hypo-
thesis, the neighbouring rocks are to be regarded as the primitive
source of the ores, the contents of a mineral vein having been leached
out of the surrounding " country."

Although this view received much support, it also encountered
much opposition, especially from the late Prof. A. Stelzner, of Frei-
'berg. Admitting that the heavy metals of the ores really exist in
some of the minerals of the neighbouring rocks — of which, indeed,
there seems no doubt — it remains a matter of discussion as to
the direction the migration may have taken place ; whether the tin
in the rock has escaped from the vein, or the tin in the vein been
drawn from the surrounding rock.

Probably there is some truth in both views. The formation of a
mineral-vein is usually so complex a process that there is room for
several explanations applicable to different phases of its develop-
ment. If the tin-ore was originally derived from deep-seated sources
by magmatic extraction, it may subsequently have become distributed

* See Laspeyres, Zdtts. f. Kryst., vol. i. (1877), p. 344 ; Kohlmann, ibid., vol.
xxiv. (1895), p. 355. " Carlsbad twins " are so called because characteristi-
cally seen in the orthoclase-felspar of the Carlsbad granite.

t In some of the Wheal Coates pseudomorphs, the felspar has been replaced
by kaolin and secondary mica, as seen in No. 48, and in certain specimens in
the Case of pseudomorphs and others in the Horse-shoe Case. For British
pseudomorphs generally see Prof. Miers in Min. Mag., vol. xi. (1897), p. 263.

1 " Untersuchungen iiber Erzgange." Von Fridolin Sandberger. Wies-
baden. 1882.

CASSITERITE. ];")

by solution ; whilst ore disseminated through a rock as an impregna-
tion may have been dissolved out, transported to a greater or less
distance, and segregated locally. The plane of weakness in a rock,
represented by a vein, has in most cases been opened again and
again, and has been the scene at different stages of very varied
activities. Dr. Flett has recently shown how complicated must have
been the history of certain brecciated veinstones in Cornwall.*

Cassiterite. (Nos. 1 to 07.)

The specimens numbered 1 to 67, exhibited in the first division
of Case 1, are (with the exception of No. 46) examples of Cornish
Cassiterite or tinstone. The crystals from Cornwall are usually
small, but some of exceptional size are here exhibited, and others
will be found among the British ores in Wall-cases 7 and 8.

Cassiterite crystallises in the tetragonal system, termed by some
writers the pyramidal, dimetric or quadratic system. f The
specimen No. 1 shows short four-sided prisms, each terminated by
a four-faced pyramid ; but crystals of such simple type are
not common. Many, if not most, of the crystals exhibited in this
case are twinned, or macled, sometimes exhibiting geniculate or
knee-shaped structures. Small paper arrows on No. 6 point to the
re-entrant angles so characteristic of twinned crystals, and
many similar, if less conspicuous, angles may be observed on other
specimens. J

Nearly a century ago, a large series of fine crystals of Cornish tin-
stone was examined by William Phillips, and described and figured
by him in an early volume of the " Transactions of the Geological
Society of London. "§ His observations enabled him to trace a local
distribution of particular types of crystals.

The colour of cassiterite, as shown by the specimens in this case, is
frequently a rich chestnut-brown, passing into a brilliant black. It is
generally said that the dark colour is due to the presence of ferric
oxide. Zonal colouration is sometimes seen in microscopic sections
of crystals of cassiterite. In Nos. 19 and 20 the crystals are trans-
lucent and of a redcolour,ratherlikesomekindsof ferruginous quartz;
but such crystals are rare. A yellowish brown tinstone, somewhat

* GeoL. Surv. Summary of Progress for 1902 (1903), p. 154.

t Crystals are classified, according to their geometrical and physioal char-
acters, in large groups called systems. Within thesa systems there are smaller
groups, based on certain types of symmetry, called classes. Six natural
systems are recognised, and thirty-two classes are possible. For modern views
on crystals the student may consult Prof. N. Story-Maskelyne's "Crystallo-
graphy " (Oxford: 1895), and Prof. W. J. Lewis's "Treatise on Crystallo-
graphy " (Cambridge: 1899). See also Prof. Miers's "Mineralogy"
(London: 1902),

% A re-entrant angle is one exceeding 180°, or greater than two right angles.

§ l " A Description of the Oxyd of Tin." By William Phillips, Tram. Geol.
Soc, voL ii. (1814), 336. Cornish cassiterite has since been the subject of
crystallography study by Prof. Becke (Min. Mit., 1877, p. 243), Dr.
Kohlmann (Zeits. j. Kryst., vol. xxiv., 1895, p. 350), and others.

1<> MINERALS OF CORNWALL AND DKVON.

translucent, is called rosin-tin. In connection with the colour of
cassiterite, attention may be directed to some white tinstone from
the Malay Peninsula presented by Cecil Wray, Esq., and exhibited
in Wall-case 40 ; whilst among the Australian minerals in Wall-case
38 will be found some yellow, brown, and red cassiterite, so trans-
parent as to be cut into gem-stones, which display diamond-like
brilliancy. The adamantine lustre of cassiterite is rather character-
istic, and the eye will be attracted by the splendent faces of many
of the Cornish crystals.

The variety of cassiterite known as sparable tin is represented by
Nos. 21 to 32. This variety occurs in sharply-pointed crystals due
to a large development of the ditetragonal, or eight-sided pyramid,
associated with a slender prism striated vertically. According to
Mr. R. H. Solly who has studied this type,* it occurs chiefly in the
Camborne district, always in close proximity to an elvan, and invari-
ably accompanied by chlorite or " peach." The common name
is said to have been suggested by the resemblance of the sharp
elongated crystals to the sparable nails used by cobblers, the
term " sparable " itself being, perhaps, a corruption of " sparrow-
bill," in allusion to the shape. Other trivial names are tooth-tin,
referring to the acute pyramidal terminations (No. 23), and
needle-tin, applied to the very slender crystals (Nos. 27, 31, etc.).

The fibrous variety of cassiterite known as wood-tin is represented
by a series of specimens (Nos. 33 to 40.) This mineral was originally
found in the form of rolled fragments in the old Cornish workings
for stream-tin, and for a long time was known only in this detrital
form. Examples of such water-worn fragments, exhibited in the
tray No. 34, show the characteristic fibrous structure, the hair-
brown colour, and the dull lustre of this variety. Many of these
pieces resemble, except in density, the fibrous oxide of iron called
" wood-iron ore" ; and old writers, struck with the resemblance of
the wood-tin to fibrous hrematite, termed it tin-hcematite.

The small pebbles of concretionary tinstone, No. 43, present a zonal
structure, similar to that of an agate, and suggest gradual formation
by a sequence of deposits. The agatiform appearance is well seen in
the large pebble with a dimpled surface, each pit here representing
the position of a former nucleus surrounded by successive rings.
Some of the small pebbles in No. 44 show the botryoidal shape of the
concretions. In the large water-worn fragment, No. 41, the wood-tin
is associated with vein-quartz, suggesting the source of the mineral .

Wood-tin in the matrix is of exceptional occurrence, but several
fine examples are here shown. The specimens in Tray No. 33, from
the Prideaux Wood mine, near Liskeard, exhibit wedge-shaped
segments of globular concretions, composed of radiating fibres with
concentric bands of pale and dark brown tints. The mineral is
extremely brittle, breaking in the direction of the fibres. These

* " Cassiterite, ' Sparable Tin,' from Cornwall." By R. H. Solly, M.A.
Mineralcgical Magazine, vol. ix. (1891), p. 199.

CASSITERITE. ]7

specimens were obtained from a lode of copper-ore, and are loosely
embedded in a brecciated matrix composed of quartz, chlorite, iron-
pyrites, copper pyrites, ani brown oxide of iron *

In the specimen Xo. 37, from Fowey Consols, small fibrous con-
cretions of pale brown wood-tin are embedded in a " peachy " vein-
stone. Xo. 38 shows a mass of cassiterite enclosing numerous small
globular concretions of wood-tin. Each globule exhibits on the
fractured surface a pale brown nucleus, surrounded by an inner
ring and an outer zone of dark divergent fibres. In this specimen
the cassiterite is associated with lamellar carbonate of lime, or
Schiefer spar, an association which is quite exceptional in Cornwall.
The specimen probably came from the Garth Mine, near Penzance,
and bears Heuland's label, dated 1839, describing it as unique.
Pebbles showing the small rings of wood-tin, in varying shades of
brown, as seen in some of the pieces in the Tray Xo. -1-i, are known as
toads' -eye tin.

In the interesting specimens Xos. 35 and 36, believed to be from
the Sancreed Mine, the wood" tin occurs in brown zones investing
quartz. The fracture of Xo. 35 has disclosed a hexagonal pyramid
of quartz, with pitted surface, completely surrounded by dark brown
fibrous tinstone, crystallised on the outside of the deposit. The
botryoidal form of the free surface of the wood-tin is well seen on
Xo. 36. The matrix seems to be an altered granitic rock, with
quartz, pink orthoclase and much cassiterite.

Xo 40 is an example of the nodular masses of tinstone with fibrous
structure, which occurred rather plentifully at one time at Great
"Wheal Vor Mine, near Helston.f At this mine wood-tin was found
as isolated masses, as scattered grains and as small veins, at a depth
of about 200 fathoms. The specimen exhibited is not ordinary
wood-tin, but fibrous cassiterite of nearly black colour, some of the
fibres, however, being brown, slightly translucent and resinous.

It has been pointed out by Mr. J. H. Collins, that ancient ingots of
metallic tin, such as those known in Cornwall as "Jews' House Tin,"
may become coated naturally with an incrustation of tin dioxide,
having microscopically a fibro-radiate and concentric structure, very
similar to that of wood-tin. %

By the disintegration of tin-lodes and other stanniferous deposits,
the cassiterite may be set free, and after transport by running water
be deposited as pebbles, gravel or even fine sand. This is the
stream-tin, which was formerly found in superficial deposits in many

* The varieties of wood-tin are fully described by Mr. J. H. Collins, F.G.S.,
in the second part of bis paper " On Cornish Tin-stones and Tin-capels."
Mineralogical Magazine, vol. iv. (1882) p. 1 (first paper), p. 103 (second paper),
and voL v. (1884), p. 121 (third paper). Reprinted, with additions and cor-
rections, and with separate pagination. Truro : 1888.

t " On the occurrence of wood-tin at the Great Wheal Vor Mines." By
G. M. Henty. Rep. Miners' Assoc. Cornwall and Devon, 1867, p. 55. " On
the occurrence of wood-tin ore in the Wheal Metal Lode at Wheal Vor in
Breage." By William Argall. Journ. B. Inst. Cornwall, vol. iv. p. 255.

+ Min. Mag., vol. iv. (1882), p. 111.

7882. C

18 MINERALS OF CORNWALL AND DEVON.

parts of Cornwall.* Several examples of this detrital tin ore are here
exhibited (Nos. 41 to 45). No. 41 is a large water-worn fragment
from a tin lode, showing the cassiterite attached to vein
quartz ; No. 42 is a tray of rather largS well-rounded pebbles ;
Nos. 43 and 44 are trays of small fragments of stream-tin including
pebbles of agatiform cassiterite and toad's-eye tin ; No. 45 is an
example of the fine sandy alluvial tin. In the sand the cassiterite
is associated with other hard and dense minerals, such as magnetite,
ilmenite and native gold, derived from the disintegration of the tin-
bearing rocks.

Probably the alluvial deposits of tin-ore in Cornwall attracted
attention in prehistoric times, and were worked as a source of the
metal before the veins themselves had been attacked by the miner.
All the old tin stream-works are now practically exhausted, though
certain patches of " tin-ground " continued to be worked until quite
a recent period. The tin-streaming carried on at the present time
along the Red River, between the parishes of Camborne and Illogan,
is confined to washing the tailings, or slimes, allowed to run to waste
from the dressing-floors of modern mines. Borings made a few years
ago in the lower part of the Red River valley, in quest of true tin-
gravels which might have been neglected by the old workers in the
district, proved the existence of undisturbed stanniferous alluvium,
though no payable patches were detected.f

Gold was found in most of the old stream-works, and the tinners
were in the habit of collecting the glittering grains and preserving
them in quills. Occasionally, though very rarely, a comparatively
large nugget was discovered. One of these exceptional pieces is here
exhibited (No. 46). This specimen, from the old stream-works of
the Carnon Valley, in the parish of Feock, near Falmouth — a
locality famous for its large nuggets — weighs 15 - 96 grams, or
10 dwts. 6 grains ; but the mass is not exclusively gold, the metal
being associated with a little vein-quartz.J

It is known that gold occurs in situ in a large number of localities
in Cornwall, though it is not generally recognised in tin-lodes. Many
years ago Arthur Dean found it in the Great Dowgas Mine, near St.
Austell, and in several lead and copper -lodes near Falmouth§ ; Mr.
John Garby obtained it from a cross-course at Wheal Sparnon, near

* On Comish stream-tin consult Henwood " On the Detrital Tin-ore of
Cornwall," Journ. B. Inst. Cornwall, vol. iv., p. 191 ; and Collins, ibid.,
vol. xii., p. 64.

t " Alluvial Deposits in the Lower Portion of the Red River Valley, near
Camborne." By F. J. Stephens, F.G.S. Trans. Qeol. Soc. Cornwall., vol. xii.
(1900) p. 324.

% Borlase states that the largest piece of Cornish gold known to him was
a specimen found in 1756, weighing 15 dwts. '16 grs. Greg and Lettsom cite
a' Cornish specimen weighing 2 ozs. 3 dwts. For British Gold, see Wall-
case No. 14.

3 " Gold in Cornwall." Rep. Miners' Assoc. Cornwall, 1865.

ASSOCIATES OF CASSITERITE. 19

Redruth ;^and the late Mr. S. R. Pattison recorded it from David-
stowe in North Cornwall.* Many other localities have been cited,
and Mr. J. H. Collins remarks that few ores and gozzans are quite
free from gold.f In recent years gold has been discovered by Capt.
Hambly in the sands of the Menaccan River and in certain gozzans
in the Gwennap district ; whilst Mr. F. J. Stephens has indicated
several localities in which he has detected gold.J In Devonshire
gold has been found at North Molton, especially in the gozzans of the
old Poltimore copper-mine. Probably in many cases the gold has
been set free on the decomposition of auriferous pyrites.

An interesting group of specimens, numbered 50 to 67, is intended
to illustrate the natural association of cassiterite with other minerals.
This relationship, frequently so suggestive in discussing the origin of
mineral deposits, is conveniently designated as paragenesis — a term
introduced more than half a century ago by the Saxon mineral-
ogist Breithaupt. § The general subject receives copious illustration
in the series of veinstones arranged in the Wall-cases 27 to 30, but
the small group of specimens immediately under review is limited to
the associates of tinstone.

The very common association of cassiterite with quarts is seen in
many of the specimens, notably in Nos. 50 to 52. In No. 51 the
tin-ore is attached to quartz which exhibits in places a beautiful
amethystine tint. No. 54 shows the tinstone in company with quartz
and apatite — the latter a fluo-phosphate of calcium. Tourmaline, a
very constant attendant on cassiterite, is seen with the tin-ore in No.
55 ; fluor-spar accompanies the cassiterite in No. 56 ; and topaz, in
distinct crystals, may be seen alongside the tinstone in Nos. 57 to 59.
The cassiterite is associated with chalybite, or carbonate of iron, in
No. 52 ; with mispickel, or arsenical pyrites, in Nos. 61 and 62 ;
with copper -pyrites in Nos. 63 and 64 ; with copper-pyrites and zinc-
blende in No. 67 ; and with iron-pyrites and blende in No. 60. An
interesting relationship is seen in No. 39, where wood-tin is seated
on delicate needle-like crystals of bitmuthite, or sulphide of bismuth.
The study of the various associates of tin-ore will be resumed in sub-
sequent pages (see especially p. 21).

* " On Auriferous Quartz-rock in North Cornwall." By S. R. Pattison,
F.G.S. Quart. Journ. Grot. Soc, vol. x. (1854), p. 247.

t " On the Origin and Development of Ore-Deposits.'' By J. H. Collins,
F.G.S. Journ. Roy. Inst. Cornwall, voL xii. (1894), p. 49.

% " The Conglomerates of Cornwall." By Captain Hambly. Rep. Corn.,
Polyt. Soc, 1897.

" Recent Discoveries of Gold in West Cornwall." By Francis'J. Stephens
F.G.S. Trans. Roy. Geol. Soc. Cornwall, vol. xii. (1898) p. 241.

For other references to the gold of Cornwall and Devon see De la Beche's
Report, p. 613 ; Greg and Lettsom's Mineralogy, p. 237 ; and Coffins' Minera-
logy of Cornwall and Devon, p. 52.

§ See his work, " Die Paragenesis der Mineralien." Freiberg : 1849.
7882. c 2

20 MINERALS OF CORNWALL AND DEVON.

Stannite. (No. 68.)

No. 68 is a typical specimen of the mineral known as stannite or
stannine, in which tin occurs to the extent of between 20 and 30 per
cent, in the rare form of a sulphide. The mineral also contains
copper and iron, frequently with zinc, and may be regarded as a com-
plex sulphide, or probably rather as a sulpho-stannate, not without
some chemical kinship to the mineral known as tetrahedrite (p. 64).*

Stannite is known also as tin-pyrites, the term " pyrites " being a
general name applied to many metallic sulphides. By miners the
mineral is termed bell-metal ore — a term suggested by the colour
which it usually presents, and which may be due to an intimate
admixture of copper-pyrites. The colour of the purer varieties of
stannite seems to be steel-grey or iron-black rather than yellowish.

This mineral was originally discovered at Wheal Rock, near St.
Agnes, and has since been recorded from a great number of Cornish
localities. At one time it occurred at Cam Brae, near Camborne,
in sufficient quantity to be raised as an ore. Granite impregnated
with tin-ore, partly in the form of stannite, has been found at Stenna
Gwyn, in the parish of St. Stephens.

Crystallised stannite is very rare, and the crystals even when they
do occur are often indistinct, so that their type of symmetry has been
open to some doubt. It has, however, been shown by Mr. L. J.
Spencer that the species belongs to the tetragonal system, and
presents forms closely related to those of copper-pyrites. | The
Cornish stannite is usually massive, though imperfect crystals, often
regarded as cubic, are not unknown.

By the decomposition of stannite the metals which it contains
may become converted into oxides and hydroxides, giving rise to a
product which has been described under the name of cwpro-cassiterite.
It has been said that in some tin lodes, the metal occurs as an oxide
in the shallow workings and as sulphide in the deeper parts. If this
really occurs, it must be quite exceptional, the normal condition of
tin-ore even in the most profound parts of a lode being that of
cassiterite. The tendency of tin to combine with oxygen rather than
with sulphur is seen in the alteration which ancient Roman bronzes
have suffered on prolonged exposure to thermal waters. Thus, at
Bourbonne-les-Bains the bronze medals showed an incrustation of
oxide of tin associated with copper sulphides — the two metals of the
alloy exposed to like conditions having yielded quite different types
of alteration-products.

It is to be regretted that the term stannite is ambiguous, inasmuch
as it has also been sometimes applied to a mineral substance which
seems to be a mechanical mixture of cassiterite and quartz. (See
No. 80, p. 23).

* " Tabellarische Uebersicht der Mineralien nach ihren krystallographisch-
chetnischen Eeziehungen : Geordnet von P. Groth." 4 Aufl. 1898, p. 39.

f " Crystallised Stannite from Bolivia." By L. J. Spencer, M.A. With
Analyses by G. T. Prior, M.A. Min. Mag., vol. xiii. (1901), p. 54.

QUARTZ. 21

DIVISION -J.

MINERALS OF CORNWALL AXD DEVON".

Minerals associated with Cassiterite.

(Xos. m to 136.)

Numerous examples of the minerals which occur in company with
the ores of tin are here grouped together, forming a much larger
collection of such minerals than is exhibited in the opposite Division
of the Case, and thus giving a wider view of their paragenetic
relations. All the specimens here exhibited have been obtained from
Cornwall and Devon, but it has not been deemed desirable to limit
the collection to specimens actually found in tin-lodes, inasmuch as
these may not in all cases fully illustrate the characters of the several
species.

Quartz. (Xos. 69 to 80.)

This is by far the most common mineral of the tin-veins, forming
in some cases the sole matrix of the ore. The vein-quartz is usually
white and opaque, rather fatty in lustre,and either compact or cry-
stalline in texture. When granular it is known to Cornish miners
as sugary spar. Microscopic cavities with liquid inclusions usually
abound. It is generally supposed that the vein-stuff must have
been deposited from solution. Thermal waters, from deep-seated
sources, circulating through the vein fissures, might carry
silica in solution and deposit it on the walls of the cavities. In those
lodes which are termed comby,* and exhibit a succession of plates of
mineral matter, more or less parallel, it is clear that the quartz,
which is usually abundant in such lodes, must have been formed in
successive deposits on the walls of the veins, inasmuch as the crystals
have their apices directed from the walls inwards, and in certain
cases the points of the crystals in opposite layers meet and engage
each other, like the teeth of two combs. Many comby lodes prove,
by their structure, that the same fissure must have been re-opened,
perhaps several times, and fresh vein-stuff deposited.

The deposition of mineral matter in parallel bands in a vein was
termed by the late Professor Posepny crustification,] since the succes-
sive deposits from a series of crusts, following each other in regular
sequence. Beautiful examples of banded or " ribband veinstones" as
well as of " comby lodes " are exhibited in Wall-cases 29 and 30.

Although the quartz in these veinstones is probably due to hydro-
thermal action, it is notable that deposits from hot springs rarely

* For description and figures of combv lodes see De la Beche's " Report
on the Geology of Cornwall, Devon, and West Somerset " (1839) pp. 339-342.

| " The Genesis of Ore-deposits." By Prof. Franz Posepny. Trans.
American Inst. Mining Engineers, vol. xxiii. (1894), p. 197. Reprinted, with
other papers on the subject, in a Eeparate volume. 1902.

22 MINERALS OF CORNWALL AND DEVON.

contain quartz. In siliceous ainter the silica usually exists in the
hydrated opaline condition ; but crystalline quartz has occasionally
been found, as in the sinter of Furnas, in the Azores, and in deposits
from the warm springs of Mauhourat near Cauterets. Temperature,
and time are no doubt important factors in the process of crystallisa-
tion. As far back as 1845 Schafhautl obtained quartz in a crystallised
condition by heating precipitated silica in a Papin's digester. In
Daubree's classical experiments, crystals of quartz, beautifully
formed, though minute, were obtained from the decomposition of
glass by means of strongly superheated water.* It has been shown,
however, by M. Kroustchoff that crystallised quartz may be
formed at a temperature less elevated than that employed by
Daubree. In- KroustchofFs experiments an aqueous solution of
silica was kept for several months in a closed vessel, and exposed
periodically to a temperature of 250°C, when crystals of quartz
were obtained, of a similar type to Daubree's, and of a very notable
size, some of the prismatic crystals reaching a length of 8 mm.|

W. Bruhns has shown that distinct crystals of quartz may be
formed by exposing either amorphous silica or powdered glass to the
action of water containing ammonium fluoride at a temperature of
300°C. for a period of ten hours. J Here the fluorine seems to act as a
mineralising agent, or agent in determining crystallisation. Much
of the quartz of the tin-lodes must have been deposited during the
early phases of their history, whilst the tin-bearing fluorine com-
pounds were in activity. It has been suggested that some of the
quartz may represent the silica set free on the decomposition of
hydrofluosilicic acid by means of water. §

During the alteration of the felspathic minerals of granitic rocks
into kaolin — an alteration not uncommon in many parts of Corn-
wall — free silica must be eliminated. Whether the decomposition
were effected by hydrofluoric acid from below or by carbonic acid
from above, the silica of the alkaline or alkaline-earthy silicate of the
felspar would, in either case, be parted from its base. The nascent
silica probably assumed in most cases an opaline state, but it is con-
ceivable that under certain conditions it might crystallise. Certain
doubly-terminated crystals embedded in china-clay, and apparently
destitute of basal attachment, have been tentatively referred to such
an origin.

The general characters of quartz will be fully considered when
dealing with the sparry minerals of the lodes displayed in Case VI.
(p. 90). In the Case under present review there is exhibited only a
small series of specimens, yet sufficient to illustrate the crystalline

* " Etudes synthetiques." Par A. Daubree. 1879, p. 164.

f " Nouvelles syntheses du Quartz et do la Tridymite." Par M. K. de
Kroustchoff. Bull, de la Soc. Fran. Min., tome x. (1887), p. 31.!)

J " Beitrage sur Mineralsyn these." Noues Jahrbuch. 1880, ii., p. 62.

§ '' Traits des Gites Mineraux et Metalliferes." Par Ed. Fuchs et L. de
Launay, Tome ii., 1893, p. 109.

APATITE. 23

characters and the varied colours of the Cornish quartz. The
beautiful tints of the purple amethyst are well seen in Nos. 77 to
79. (For amethyst see p. 92.)

In the tray, No. 8l), are two specimens of the mineral substance
from St. Agnes unfortunately called stannite— unfortunately, because
the same name has been given to the tin-copper-iron sulphide known
as bell metal ore, described on p. 20. The so-called stannite, No. 80,
seems to be a mechanical mixture of quartz and cassiterite, but has
sometimes been described as a silicate of tin. One specimen here
exhibited is massive, and the other crystallised. The crystals are
six-sided prisms resembling those of quartz, and have been regarded
as imperfect pseudomorphs.

Although stannite is not truly a silicate of tin it is interesting to
note that a silicate containing tin and calcium from Cornwall has been
described by Dr. A. Hutchinson, of Cambridge, who has named it
Stokesite after the late Sir G. G. Stokes. The unique specimen on
which the species was founded occurred on axinite, from St. Just,
and in its appearance was suggestive of gypsum, but crystallised
in the orthorhombic system.*

Apatite. (Xos. 81 to 96.)

Although apatite was recognised as a distinct mineral species by
the Saxon mineralogist, Werner, at least as far back as 1786, and
was soon afterwards found, by the analyses of Proust and of
Klaproth, to be a phosphate of lime, yet it was not until 1827 that it
became recognised, through the work of Gustav Rose, that the phos-
phate in this mineral was associated with either a chloride or a
fluoride of calcium, or with both. Hence two varieties came to be
distinguished — chlor-apatite and fluor-apatite, of which the latter is
the more common. The mineral which accompanies the Cornish
tin ore is a fluor-apatite — a fact harmonising with the part which
fluorine is believed to have played as a vehicle of tin.

In the south of Norway veins of apatite are very numerous, and
Prof. J. H. L. Vogt has instituted an interesting comparison and
contrast between these veins and those which carry tin ore.f Both
occur in plutonic rocks, but the cassiterite-veins in rocks of acid type,
like granite ; the apatite-veins in basic rocks, like gabbro. Whilst
fluorine was active in the extraction of tin from the acid magma,
chlorine appears to have been the chief agent in extracting the
minerals of the apatite veins from the basic magma. Hence the
Norwegian phosphate is a chlor-apatite,. and that of the tin-lodes a
fluor-apatite. The apatite-veins carry titanium — a metal having
certain chemical relations with tin ; and both metals occur in the
veins as dioxides — the tin as cassiterite, the titanium as rutile. The

* " On Stokesite, a new mineral containing tin, from Cornwall." By A.
Hutchinson, M.A. Min. Mag.,\o\. xii. (1900), p. 274.

t " Problems in the Geology of Ore-deposits." Trans. Amer. Inst. Min.
Eng., vol. xxxi. (1902), p. 125.

24 MINERALS OF CORNWALL AND DEVON.

pneumatolytic action concerned in the formation of the tin- veins has
metamorphosed the neighbouring granite into greisen — an acid
felspar being partly converted into topaz, which is a mineral contain-
ing fluorine ; whilst similar action in the case of the apatite-veins
has converted a basic felspar into scapolite, a mineral containing
chlorine. Dr. Vogt has estimated that in the tin-lodes there is at
least 100 times, and perhaps 1,000 times, as much fluorine as chlorine,
while in the apatite veins these proportions are reversed.

Although apatite is a characteristic associate of tin-ore in Corn-
wall, it is by no means common in well-defined crystals. Its direct
association with cassiterite may be seen in No. 81, and again in No.
54. It is a mineral widely distributed tiu-oagii igneous rooks,
especially those of basic type, but usually in only microscopic
crystals. Apatite is characterised by much stability, and must have
crystallised out of the magma at a high temperature. That it
belongs to the first phase of consolidation is evident from its common
occurrence as inclusions in all other essential minerals, even in
magnetite, which itself is generally one of the earliest to separate.

The specimen No. 88 shows the apatite in association with axinite,
from the " greenstone " cliffs near Botallack. In No. 83 the apatite
occurs in short six-sided prisms, of beautiful blue colour, associated
with lithia mica, from St. Michael's Mount. The granite at this
famous locality is traversed by miniature tin-lodes, the walls of some
of the joints being studded with crystals of quartz, cassiterite,
wolfram, apatite, topaz and even beryl, whilst the band of granite
adjacent to the vein has been converted into greisen. The late Sir
W. W. Smyth said that " there was scarcely anywhere another
100 fathoms square of rock which presented so much of interest to
the geologist and mineralogist as this sea-beaten foreshore of St.
Michael's Mount."*

The finest examples of apatite shown in this collection are those
from near Bovey Tracey, in Devonshire (Nos. 85 to 92). In some
of these specimens the apatite appears in opaque cream-coloured
crystals, measuring more than an inch in length," each crystal being
simply a six-sided prism terminated by the basal plane. The
mineral occurs in granite, and is associated with fine crystals of black
tourmaline, as seen notably in Nos. 89 to 91.

The variety of apatite called Francolite, of which specimens 93 to
96 are examples, received its name from Wheal Franco, near Tavis-
tock, in Devonshire, where it was originally found. f Prof. N. S.
Maskelyne and the late Dr. Flight showed that in some kinds of
francolite the calcium phosphate of the fluor-apatite is partially
replaced by calcium carbonate. j No. 96 is a specimen of this

* " Remarks on the Geology of St. Michael's Mount, by Warington W.
Smyth, F.R.S., at the Annual Excursion of the Mining Association and
Institute of Cornwall." Proceedings of the Assoc, vol, i., part 3, 1887.

t " On Francolite, a supposed New Mineral." By T. H. Henry, Esq.,
F.R.S. Phil. Mag., vol. xxxvi. (1850), p. 134.

% Journ. Chem. Soc, [2] vol. ix. (1871). p. 3.

TOPAZ. 25

nature.* All the examples of francolite shown here were obtained
by the late Mr. Tailing from Fowey Consols, near Lostwithiel. It
will be seen that in some of these specimens the mineral occurs in the
form of small white hexagonal plates, with curved faces. Franco-
lite from deep workings at Levant Mine, St. Just, has been described
by Mr. R. H. Solly.f

Topaz. (Xos. 97 to 99.)

Topaz occurs in certain granitic rocks, perhaps in some cases as an
original constituent, and is not uncommon in the rocks of the West
of England. Dr. Teall has described its occurrence in a variety of
granite from Meldon, near Okehampton, in Devonshire. J In most
cases topaz is a secondary mineral, resulting usually from the
alteration of felspar. It is a characteristic constituent of the greisen,
or altered granite which occurs in the neighbourhood of certain tin-
lodes. In the process of kaolinisation, part of the silica and all the
alkaline base are removed from orthoclase ; and a somewhat similar
change, with addition of fluorine, might produce an aluminium,
fluo-silieate like topaz. In this mineral fluorine exists to the extent
of 17 or IS per cent. Prof. Penfield has shown that the fluorine may
be partially replaced by hydroxy!. § Such a medium as hydro-
fluoric acid would probably be competent, under certain conditions,
to effect the conversion of felspar into topaz. In the well-known
synthetical experiments by Daubree, a substance analogous to topaz
was formed by the action of fluoride of silicon on alumina at a white
heat. |[ Topaz has been artificially prepared by MM. Friedel and
Sarasin by the action of hydrofluo-silicic acid on silica and alumina,
with water, at a temperature of 500°C.

Whilst topaz is in many cases a mineral of secondary origin, it
tends itself to suffer alteration, and to pass into kaolin and micaceous
minerals like sericite.

The specimens of topaz here exhibited represent its occurrence at
Cligga Head, (Nos. 97 and 98) and at St. Michael's Mount (No. 99).
Other specimens from the latter locality will be found in the opposite
division of the case (Xos. 57 to 59).

The occurrence at Cligga Head, between St. Agnes and Perranporth
on the north coast of Cornwall, has been studied by Mr. J. B.
Scrivenor, whose paper on this subject has already been referred to. If
The topaz occurs on the face of the joints in the altered granite. The

* " Xote on Francolite." By F. H. Butler, M.A., A.R.S.M. Min. Mag.,
vol. vii. (1887), p. 164.

t Min. Mag., vol. vii. (1887), p. 57.

% " British Petrography." By J. J. Harris Teall, JI.A. 1888, p. 316.

§ " On the Chemical Composition and related physical properties of
Topaz." By S. L. Penfield and J. C. Minor, jr. Am. Journ. Sc, vol. xlvii.
(1894), p. 387.

|| " Etudes Synthetiques de Geologie experimentale." Par A. Daubree,
1879, p. 57.

U Quart. Journ. Geol. Soc, vol. lix. (1903), p. 142.

26 MINERALS OF CORNWALL AND DEVON.

occurrence at St. Michael's Mount is similar. The crystals are colour-
less or of pale blue tint, and some of the specimens, where not dis-
tinctly crystallised, might be mistaken on a cursory inspection for
quartz. Topaz, however, crystallises in the orthorhombic system,
and the crystals usually present, as seen here, a prismatic habit, the
prisms being striated longitudinally and presenting a perfect basal
cleavage.

In connection with the West of England topaz it may be men-
tioned that the mineral occurs also in the granite of Lundy Island.*

Fluorite. (Nos. 100 to 104.)

Whilst fluorite, or fluor-spar, is the most widely distributed of all
minerals which contain fluorine, it is not so common in the tin mines
of Cornwall as might have been anticipated. Many tin -lodes, especi-
ally in the West of Cornwall, seem destitute of fluor-spar, whilst many
veins rich in fluor-spar carry no tin. Most of the crystallised speci-
mens, such as the fine series exhibited in Case V., have been obtained
from the copper-veins and lead -veins of Cornwall and Devon. The
full description of the mineral will, therefore, be deferred until that
Case comes under review (see p. 85).

The specimen No. 100 shows the fluor-spar in direct association
with cassiterite. The spar is known to Cornish miners as Cann.

In the " china stone," or altered granitic rock worked in the neigh-
bourhood of St. Austell, the walls of the joints are sometimes lined
with deep purple fluorite. The mineral seems to be connected with
the tin-carrying fluoric compounds, which were probably responsible
for much of the alteration. Dr. Boase recorded fluor-spar from the
Hensbarrow granite. Fluorite rarely occurs as a rock constituent,
but it was found by the late Mr. R. N. Worth in a granitic rock on the
north-western flank of Trowlesworthy Tor, on the skirts of Dart-
moor, whence he called the rock Trowlesworthite.'f This is an
aggregate of bright red orthoclase, deep violet fluorite, black acicular
tourmaline, and a very little quartz. Prof. Bonney, who examined
the rock microscopically, believes that trowlesworthite has been
formed from the normal granite of the district by the replacement of
quartz by fluor-spar.:]:

Fluellite. (Nos. 105 to 109.)

Several specimens of this extremely rare mineral are here exhibited.
It was first detected eighty years ago by Levy, § and examined by
Wollaston, who found that it contained fluorine and aluminium.

* " On the Occurrence of Topazes in Lundy Island." Letter by Mr. S. G.
Perceval in Geol. Mag., vol. vii. (1870), p. 192.

t Trans. Roy. Geolog. Soc, Cornwall, vol. x. (1887), p. 177.

% Ibid., p. 180 ; also, Min. Mag., vol. vi. (1884), p. 48.

§ " On a new Mineral Substance." Ann. Phil, [n.s.] vol. viii. (1824),
p. 241.

MICAS. 27

An analysis made by Dr. Brandl, at Prof. Groth's request, has con-
firmed this determination, and proved that the mineral is a hydrated
fluoride of aluminium.*

Stenna Gwynn, near St. Austell, is the only known locality. Here
it occurs in very small crystals, of pyramidal habit, belonging to
the orthorhombic system. These are seated on a quartzose
matrix, and associated with cassiterite, fluorite, uranite, muscovite,
and wavellite. TTuellite therefore takes its place in company with
the other fluorine-bearing associates of tin-stone.

Lithia Mica. (Xo. 110.)

Lithium-bearing micas are rather characteristic of granites which
carry tin -stone and tourmaline. The typical mica, called — from its
occurrence in scaly aggregates — Lepidolite, usually presents a lilac or
rose-colour, with a rather pearly lustre on the cleavage planes. The
presence of a little manganese seems to be responsible for these tints.
The amount of lithium may reach 5 per cent, and of fluorine 8 per
cent. Boron is also usually present, as in several other minerals
friendly to tin-stone.

A lithium-iron mica, occurring characteristicallyin the stanniferous
rocks of Zinnwald, in Bohemia, is known as zinnwaldite, and some of
the Cornish micas in silvery hexagonal plates may be referable to
this type. The Zinnwald mica has been found to contain rubidium,
coesium and thallium. The presence of tin has also been recorded
in certain lithia-micas, and in some cases it appears to be present in
the form of microscopic inclusions of cassiterite.

Gilbertite. (Xos. Ill, 112.)

A yellowish or greenish micaceous mineral, observed originally at
Stenna Gwynn and since found in several china-stone districts in
Cornwall, as at St. Austell and Breage, has been distinguished by
the name of Gilbertite — a name given by Dr. Thomas Thomson, in
compliment to Davies Gilbert, the " Cornish philosopher," who was,
at one time President of the Royal Society (b. 1767, d. 1839.) The
specimens here exhibited show the mineral in stellate aggregates
of pearly scales. Being rather unctuous to the touch, it has some-
times been mistaken for talc.

Gilbertite appears to be an alteration-product of felspar, and
pseudomorphs of gilbertite in the form of orthoclase are known. It
is probable, as Mr. F. H. Butler remarked, that in some cases the
gilbertite represents one of the stages in the gradual kaolinisation of
orthoclase. f

The specimen No. 112 shows an association of gilbertite with
crystals of apatite.

* " Beitrage zur Kenntniss der natiirlichen Fluorverbindungcn." Von
P. Groth. Zeitsch. f. KrystattograpMe, vol. vii. (1883), p. 482.
f Min. Mag., vol. vii., p. 79.

28 MINERALS OF CORNWALL AND DEVON.

Tourmaline. (Nos. 113 to 120.)

Tourmaline is perhaps, with the exception of quartz, the most con-
stant associate of tin-ore. Doubt has, however, been sometimes
expressed as to such a relationship.* It is true that crystals of
tourmaline are not commonly to be seen in the lodes, but the mineral
is nevertheless present in microscopic crystals distributed through
the rocks of most tin-districts. Rocks which are stanniferous,
whether granite or lallas, are almost invariably tourmaliniferous.
The tin cupels, which are bands of altered rock, adjacent to the veins,
and generally found near the junction of the granite and the killas,
are always rich in tourmaline. The mineral is chiefly developed
near the margin of intrusive masses of granite, and in the zone of
contact-metamorphism. It appears to have been formed by the
action of vapours containing boron and fluorine, attacking the
felspathic and micaceous constituents of the rocks.

Tourmaline is a boro-silicate of complex and variable constitution,
containing aluminium, iron, magnesium and the alkali-metals, with
fluorine and hydroxyl. The proportion of boric oxide generally
ranges between 8 and 10 per cent., but may rise higher. Free boric
acid is not uncommon in the exhalations from fumaroles, notably in
those of Tuscany. Mr. Donald MacAlister has suggested that the
metaborate of sodium, formed by the action of boric acid on the
felspars, might have been an active chemical agent in the transport
of tin.f

According to a striking calculation by Mr. J. H. Collins, the tourma-
line-bearing rocks of the West of England contain something like
2,480,000 tons of fluorine for each yard in depth. J This result is
based, however, on the liberal estimate that the tourmaline contains
an average of 2 per cent, of fluorine, and that the mineral constitutes
10 per cent, of the rock.

Most of the tourmaline of Cornwall and Devon, though coloured
in thin sections, appears black when viewed in mass by reflected
light. This black, ferriferous tourmaline is known as schorl.^ It
frequently occurs in acicular crystals or in fibrous masses (No. 119).
In No. 118 the slender crystals are grouped in stellate aggregates.
Tourmaline belongs to the hexagonal system, and commonly assumes
the form of three-sided prisms, striated longitudinally, giving on
transverse section characteristic triangular figures, and carrying

* " La Tourmaline, loin d'aooompagner regulierement l'oxyde d'etain,
semble exercer sur lui une action repulsive." " Note surla Constitution des
gites stanniferes de la Villeder (Morbihan)." Par M. Lodin. Bull. OMog.
Soc. Fr. [3 serie], t. xii. (1884), p. 645. M. Lodin holds that the views of
Daubree are not applicable to the tin-deposits described in this memoir.

| " Tin and Tourmaline." By Donald A. MacAlister, Esq. Quart. Journ.
Geol. Soc, vol. lix. (1903), p. 53.

% " On the Origin and Development of Ore-deposits in the West of Eng-
land." By J. H. Collins, Cap. Ill, Journ. Roy. Inst., Cornwall, voL xi. (1893),
p. 371.

§ The word schorl is said to be derived from' the old German mim^s, and
tourmaline from the Sinhalese.

TOURMALINE. 29

rhombohedral faces at their extremities. The mineral is remarkable
for its hemimorphism,* for its pyroelectric properties and for its
optical characters. A fine series of specimens, mostly from foreign
localities, and including many gem stones, will be found in the Horse-
shoe Case, Section R.

Magnificent crystals of black tourmaline were obtained many years
ago from a small quarry of red granite not far from Bovey Tracey in
Devonshire.f Examples of these bold crystals are here exhibited as
Xos. 113 to 110. They were embedded in a matrix of ochreous clay
in a cavity of the granite, and were associated, as will be seen in these
specimens, with crystals of quartz and apatite. The crystals of
tourmaline are mostly short stout prisms, with rhombohedral ter-
minations ; and it is notable that whilst some of the faces are smooth
and brilliant others are rough and dull. In Xo. 115, and in some of
the other specimens, the apatite appears to have been formed after
the tourmaline.

The beautiful rock described by Professor Bonney under the name
of Luxullicmite is rich in tourmaline. J This rock consists of pink
orthoclase, in large twin crystals, embedded in a dark matrix of
schorl and quartz. Boulders of the rock are found at Luxullian,
near Lostwithiel, and the largest known mass was used for the
sarcophagus of the Duke of Wellington in St. Paul's. Specimens
may be seen in the Rock Collection, and some beautiful polished
examples will be found among the ornamental stones in the
Hall.

In many of the Cornish granites, tourmaline displaces, to a greater
or less extent, the micaceous and felspathic constituents, having
probably been formed at their expense, and when the replacement is
complete the resulting aggregate of quartz and tourmaline is known
as schorl-rock. Such a rock is associated, in several localities, with
the occurrence of tin-stone. Spheroidal masses of schorl-rock may
occur as enclosures in the normal granite.

Whilst tourmaline may be formed by the alteration of micaceous
minerals, there are circumstances under which it seems to be itself
changed to mica. Topaz may likewise be an alteration-product of
tourmaline. As a rule, however, the mineral is characterised by
much stability, and when set free by the disintegration of a rock it
may survive in the form of rolled fragments and be ground down as
sand. Mr. A. Dick found that about one-tenth per cent, of the
Lower Bagshot sands of Hampstead Heath, north of London, con-
sisted of grains and crystals of tourmaline. §

* Crystals are said to be hemimorphic when their opposite extremities are
dissimilarly developed, or, technically, when they possess axes of symmetry
which are polar. Hemimorphism is often correlated with pyro-electric
properties.

t " On the Mineral Localities of Devonshire.'' By Townshcnd M. Hall.
Trans. Devon. Assoc, vol. ii. (1868), p. 332.

+ Min. Mag., vol. i. (1877), p. 215.

§ Nature, vol. xxxvi. (1887), p. 91.

30 MINERALS OF CORNWALL AND DEVON.

Axinite. (Nos. 121 to 124.)

Axinite is a boro-silicate of complex composition, rather like
tourmaline, and originally regarded as a kind of schorl. It differs,
however, from tourmaline in occurring usually in basic eruptive
rocks rather than in those of acid type, though not altogether un-
known in the latter.

If the Cornish specimens are not comparable for beauty with the
fine crystals of axinite from Dauphiny they yet illustrate sufficiently
the general characters of the species. They occur as clove- brown
brilliant crystals, belonging to the anorthic system, with the sharp
axe-like edges that suggested to Haiiy the specific name.

The Dauphiny crystals, of which specimens may be seen in the
Horse-shoe Case (Section 0) occur in a zone of amphibolite and
chlorite schists.* Those of Cornwall are typically developed in the
greenstones and hornblende schists displayed in the cliffs north of
Botallack Head, at Wheal Cock and at Trewellard, north of St. Just.
Some of the specimens here shown are from Terrace Hill, Lost-
withiel. Pseudomorphs of chlorite after axinite are recorded from
Dartmoor and from St. Just. The Cornish axinite has been analysed
by Mr. J. E. Whitfield.f

Wolframite. {Nos. 125 to 130.)

Wolfram, or Wolframite, is a mineral which in Cornwall, as in so
many other parts of the world, follows close in the train of the tin-ore.
In some of the Cornish tin-lodes it has been found " inconveniently
plentiful," inasmuch as it is not easy to separate it from the tin stuff
by mechanical dressing, the specific gravity of the wolfram standing
very near to that of cassiterite (about 7). Magnetic separation has
recently been used.

Wolfram occurs usually in opaque brownish-black cleavable
masses, with a lustre so brilliant as to be almost adamantine.
Occasionally it occurs in crystals, as seen in these specimens, which
show the crystallised wolfram associated with quartz. Formerly
the crystals were regarded as orthorhombic, but they are now claimed
by the monoclinic system. Wolfram is an iron and manganese
tungstate, containing when pure about 60 per cent, of the metal
tungsten or wolframium. It is used in the preparation of tungsten-
steel, a small proportion of tungsten being found to increase the
hardness and tenacity of the metal.

Wolfram is raised to a limited extent from several mines in Corn-
wall — Cam Brea, Tin Croft, East Pool and Agar United Mines.
The quantity raised in the year 1901 was, according to official
statistics, 21 tons, valued at £408.

* " Mineralogie de la France et de aes Colonies." By A. Lacroix, vol. i.,
p. 277. Paris, 1893.

t Amer. Journ. Sc. [3], xxxiv. (1887), p. 286.

SCHEELITE : MISPICKEL. 31

By exposure to influences which remove the iron and manganese,
wolfram becomes encrusted with a yellowish earthy coating of
Wolframme or wolfram ochre, known also as tungstite. This mineral,
consisting of tungsten trioxide, is seen on specimen Xo. 132, from
East Pool Mine.

Scheelite. {Xo. 131.)

Scheelite is a calcium tungstate not common in Cornwall, but
occasionally occurring as an alteration-product of wolfram. The
two isolated crystals of this species shown here are little bipyramids,
which, notwithstanding their resemblance to regular octahedra,
belong to the tetragonal system. The other specimen in the tray,
Xo. 131, is an example of scheelite, in a chloritic matrix, from Wheal
Friendship, near Tavistock in Devonshire.

The species will be again referred to in connection with the much
finer specimens which occur in Cumberland (p. 153).

Mispickel. (Xos. 133 to 136.)

The solfatanc emanations which appear, from so many lines of
evidence, to have arisen from an acid magma and to have been active
in the formation of the deposits of tin ore in the West of England,
must have been laden not only with fluorine and boron but likewise
with sulphur and arsenic. The latter elements combined with iron
constitute the mineral called Mispickel — one of the most constant
associates of tinstone.*

In Case V there is a series of metallic sulphides, headed by the
commonest species known as iron-pyrites. The name pyrites has
come to be used as the designation of a group of related minerals, all
sulphides with a metallic aspect, and in this group mispickel is
included. It is, therefore, known, from its composition, as arsenical
pyrites, or, since pyrites is called by Cornish miners " mundic," the
mispickel is known also as arsenical mundic. The term " mispickel"
itself comes from an old German name for this, or a similar mineral.

Mispickel is an arseno-sulphide of iron, generally showing, when
freshly fractured, a white colour and metallic lustre. It crystallises
in the orthorhombic system, frequently in twin crystals. Further
description of the species will be found in connection with the section
dealing with pyrites (p. 62).

* A soljaiara ought literally to exhale vapours containing sulphur (Italian
solfo). Vapour- vents emitting, at a higher temperature, chlorine compounds
are often termed fumaroles ; but the nomenclature is lax. Pneumatolytic
emanations were evolved from the deep-seated magma, under pressure.
Probably the fluorine-bearing vapours concerned in the production of tin-
ore came from the hottest subterranean fumaroles ; and it has been supposed
that the sulphur-carrying vapours represented a rather cooler phase of
emission.

On the genesis of ore-deposits see Prof. J. F. Kemp's paper on -' The Role
of the Igneous Rocks in the Formation of Veins." Trans. Am. Inst. Jlin.
Eng., vol. xxxi. (1902), p. 169.

32 MINERALS OF CORNWALL AND DEVON.

Although mispickel occurs in both tin-lodes and copper-lodes in
the West of England, it seems to be more common in the former. It
is generally found in veins running through killas near to granite, but
is not common in the granite itself. In some Cornish mines it seems
to have great vertical persistence, increasing in quantity down-
wards, and thus leading to the inference that it may be a vein
mineral of very early formation.

Arsenical pyrites is still raised in Cornwall and Devon, though to a
less extent than formerly. During the year 1901 the quantity of the
mineral raised in Cornwall was 2,334 tons, and in Devonshire 244
tons. This arsenic ore is roasted for the production of arsenious
anhydride, or " white arsenic." According to the official statistics,
the amount of arsenic, partly as " soot " and partly as " white
arsenic," refined at the mines, and obtained principally from the
arsenical pyrites of the tin and copper mines, was 1,258 tons in Corn-
wall and 2,103 tons in Devonshire.

COPPEK-ORES. 33

CASE II.

DIVISION 1.
MINERALS OF CORNWALL AND DEVON.
Copper Sulphides and Sulpho-ferrites.
(Nos. 137 to 204.)

The ores of copper, next to those of tin, are the most important
metal-bearing minerals yielded by the mines of the Damnonian
Peninsula. In the early days of Cornish tin mining the copper-ores,
which were not infrequently found in association with those of tin,
were altogether neglected. Carew, writing in the beginning of the
seventeenth century, says : " Copper is found in sundry places, but
with what gain to the searchers I have not been curious to enquire
nor they hasty to reveal."* After Carew's time a hundred years had
to pass before the copper-ores of Cornwall came to be systematically
worked.

At one time it was believed that the ores of copper in Cornwall
were restricted to the western part of the peninsula — a belief which
found expression in the saying " No copper east of Truro Bridge."
That idea was dispelled, however, long ago ; and mines of great
value have been worked far beyond the old restricted limit. Never-
theless, the most important workings for copper at the present time
are in the extreme west. During the year 1902 Levant Mine in
St. Just turned out not less than 3,056 tons of dressed copper ore.

No sharp line of separation can be drawn between the deposits of
copper-ore and those of tin. The lodes run in the same general
direction, and in many cases the same vein may carry both tin and
copper. The specimen, No. 137, shows the association of copper
pyrites with crystals of cassiterite. Some mines have been worked
at one time for tin, at another for copper ; and it has not infrequently
happened that copper-lodes have carried more or less tinstone
in their upper or gozzany part. Certain mines which were worked
originally for tin ore have yielded copper ore at lower levels,
and then at yet greater depths the copper has given way to tin. It
has been said that in many rases the copper minerals seem to have
been of later introduction than the tin ore, but it is doubtful whether
such a conclusion admits of wide application. Mr. J. B. Hill believes
that the copper and tin are of " approximately identical age," +

* Survey of Cornwall. Ed. 1811., p. 21.

t Trana. R. Geol. Soc. Corn., vol. xii., part vii. (1902), p. 593.

7S&2. D

34: MINERALS OF CORNWALL AND DEVON.

whilst Mr. D. MacAJister thinks, with reference to the Camborne
district, that " probably the copper arrived either before the tin, or
at the same time."*

It has been observed that in mixed deposits the copper generally
occurs where the vein traverses killas, whilst in granite it may be dis-
placed by tin. Some of the lodes, for instance, near Tavistock, in
Devonshire, produced copper while in killas, but only tin after pass-
ing into the Dartmoor granite. At the junction of the two rocks,
rich bunches of copper-ore have sometimes been found, and they
have also occurred in the killas far from any visible granite.

The primary condition of the copper in the veins of Cornwall and
Devon, as in many other copper-mining localities, appears to be that
of copper-pyrites — a sulphide of copper and iron, containing theoretic-
ally about 34 per cent, of metallic copper. In the higher part of the
vein the pyrites may be associated with, or even replaced by, the
richer copper sulphides known as purple ore and copper glance,
The sulphides thus become progressively richer in copper as thej
approach the surface — an enrichment probably due, at least in part,
to the removal of the iron sulphide in the copper-pyrites, by means of
solution. The succession of minerals may be represented in descend-
ing sequence as follows, though the order may be subject to much
local irregularity.

Copper glance (Chalcocite), with 80 per cent, of copper.

Purple copper ore (Erubescite), „ 55 „ „

Copper pyrites (Ghalcopyrite), „ 34 „ „

It is worth noting that at the famous copper mines of Monte Catini,
in Tuscany, there are nodules of ore which show a succession of
minerals arranged in zones following the same order. The central
part of the nodule is copper pyrites, which passes into purple ore,
and this gives way towards the exterior to copper glance, whilst even
native copper may appear on the surface.

It seems fair, however, to point out that successive changes of
precisely the inverse order may be traced on metallic copper after
prolonged exposure to the action of thermal waters. Roman bronze
coins, for example, found in the spring of Bourbon-PArchambault, in
Central France, have exhibited a central core of unaltered metal,
followed from within outwards by successive zones of copper glance,
purple ore and copper pyrites."} - Mr. S. F. Emmons has observed
that as the tendency to establish a condition of chemical equilibrium
inareaction may be modified by varying conditions of temperature,
pressure and strength of the reacting solutions, it is conceivable that
the reaction may proceed in the reverse direction under altered con-
ditions.

The concentration of copper in the region of rich sulphides may be
due, not only to the removal of the iron from copper-iron sulphides,
but also to the direct deposition of copper sulphide from circulating

* Trans. R. Geol. Soc, Corn., vol. xii., part viii. (1903), p. 773.
f Comptes Bendus, vol. lxxx. (1875), p. 1297.

CHALCOPYTUTE. 35

solutions. This secondary enrichment has been ably discussed by
such geologists as Prof. S. F. Emmons* and Mr. W. H. Weed.t Near
the surface copper-pyrites would be prone to oxidation, and the
copper sulphate so formed and carried downwards in solution might
suffer reduction not only by organic matter but by such metallic
sulphides as iron pyrites, and thus a precipitate of fresh sulphide of
copper might be produced.

In the copper-veins of Cornwall, as pointed out by the late Mr.
Arthur Collins, three zones may be roughly recognised, though in
many cases they are by no means sharply separated :

1 . Z^me of oxidation or weathering, which will be described under

the head of gozzans (p. 41).

2. Zone of sulphide enrichment, in which the secondary sulphur-

etted ores have been produced.

3. Zone of primary sulphide, which may be copper-pyrites, or

poor cupriferous iron pyrites.

In the West of England the rich ore-belts have in many cases been
passed through, and a region of impoverished ore has been reached.
" Copper mining," wrote Sir C. Le Xeve Foster,* " is an industry
which is rapidly decreasing in importance in Britain." During the
year 1902, the mines of Cornwall produced 4,547 tons of dressed
copper ore, valued at £12,374 ; whilst in Devonshire only 350 tons
were raised, having a value of £037.

Chalcopyrite. (Nos. 137 to 164.)

The most common ore of copper in the mines of the West of Eng-
land, as in so many other localities, is a combination of copper, iron
and sulphur, constituting the mineral usually known as Copper-
pyrilcs. By mineralogists it is now generally designated by
Beudant's name Chalcopyrite. A suggestion made long ago by
Brooke and Miller that the mineral should be termed Toi/rmite,
after Wheal Towan, a mine near St. Agnes, which yielded fine
crystals of this species, is a suggestion which was never widely
adopted. By miners the mineral is generally known as yellow are.
When the tinstone of a lode is replaced by a deposit of this ore, the
miner would say that " The yellows cut out the tin."

Chalcopyrite crystallises in the tetragonal system, usually in
hemihedral forms.; The crystals present a sphenoidal habit, with
the faces in many cases curved and striated. Twin crystals are

* " The Secondary Enrichment of Ore-deposits.' - Trans. Am. Inr-t. Minimj
Eng., voL xxx. (1901), p. 177.

+ " The Enrichment of Gold and Silver Veins." By Walter Harvey Weed,

Ibid., p. 424.

% Home Office Report (part III., Output). 1903, p 200.

S A Hemih'-drnl form is one in which only half the number of faces
required by the full symmetry of its system are developed. It may be re-
garded as formed from a holohedral form by the symmetrical suppression of
half the faces.

7>s82. r> 2

36 MINERALS OF CORNWALL AND DEVON.

common. The angles of the sphenoid are so close to those of the
regular tetrahedron that the species was referred to the cubic system
until the measurements of William Phillips, aided by Levy, in 1822,
showed that " pyritous copper " was not cubic* At the same time
the mineral was carefully analysed by his brother Richard Phillips.
Crystals of Cornish chalcopyrite have been studied by Mr.
L. Fletcherf and by Professor J. W. LewisJ, not to mention
continental crystallographers. For good crystals, see Nos. 138
to 153.

Although crystals of chalcopyrite are common enough in collec-
tions, the mineral usually occurs in the Cornish lodes in compact or
amorphous masses. In some cases it presents mammillary and
botryoidal forms, which are known as Blister ore. Such forms are
seen in Nos. 161 to 164.

Chalcopyrite presents a rich golden yellow colour, but tends to
tarnish on exposure. The tarnish is sometimes brilliantly iridescent,
when the mineral becomes known as peacock ore (Nos. 154, 155).
Iron-pyrites may be associated with copper-pyrites as an intimate
mechanical mixture, and in this way the latter loses its character-
istic colour, becoming much paler. The two kinds of pyrites are
distinguished not only by colour but by hardness, the copper-pyrites
yielding readily to a knife whilst the iron-pyrites is too hard to be
scratched by a steel point.

In chalcopyrite tie three constituent elements are present in
nearly equal proportions. The formula for chalcopyrite, CuFeS.,,
yields : copper 34 ■ 6 per cent., iron 30 • 5, and sulphur 34' 9 ; but
analyses often show an excess of iron, probably due to admixture
with iron-pyrites.

It is usual to regard chalcopyrite as a double sulphide of copper
and iron, and since it yields, by alteration, copper glance (Cu 2 S)
it is supposed to contain a molecule of cuprous sulphide, whence its
formula is often written Cu 2 SFe :S S 5 . But chalcopyrite may also be
viewed as a sulpho-ferrite ; that is to say, it may be regarded as a
derivative from a sulpho-acid, FeS 2 H, by replacement of the
hydrogen by univalent copper.§

The recent formation of copper'pyrites has been illustrated by the
action of thermal waters on objects containing copper. Thus, at
Bourbonne-les-Bains and at Bourbon-rArchambault, in Central
France, copper-pyrites has been formed on old Roman bronze coins.
The sulphur in such eases is supplied by the sulphates which the

* " On the Crystalline Form of Yellow Copper Ore." By William Phillips.
Annals Phil, [n.s.], vol. iii., p. 296.

f " Crystallography Notes." iiy L. Fletcher, M.,\. Proc. Cri/tlri!-
lologir.nl Svr.. part ii. (1882;, p. 11-1. Also Cloth's Zeitsch. Krysl., Bd. vii.
(1883), p. 321.

% '" On some remarkable Composite Crystals of Copper Pyrites from
Cornwall." By Prof. W. J. Lewis, M.A., and A. L. Hall, B.A. Min. Mag.,
vol. xii. (1890), p. 324.

§ " Tabellarische Uebersicht der Mineralien naoh ihreri krystallographiseh-
chemisohen Beziehungen. Geordnct von P. Groth." 4 Auf., 1898, p. 29.

CHALCOCITE. 37

waters contain, and which are reduced to sulphides by the decom-
position of organic matter. Crystals of copper-pyrites have also
been formed inside the copper tubes used for conveying thermal
waters near Pest. *

The paragenetic relations of copper- pyrites are well illustrated by
the specimens in the Case under review. Xo. 137 shows chalco-
pyrite and cassiterite side by side. The common association with
quartz is seen in many of the specimens, notably in Xos. 139, 146,
140, 150, and 153. With calcite the Cornish chalcopyrite occurs
much less frequently, but examples are shown from the Caradon
mines in Xo. 147. Chalybite, or carbonate of iron, is a frequent com-
panion of copper-pyrites, as seen in Xos. 142 and 145. In Xo. 158
chalcopyrite is associated with fluor-spar ; in Xos. 140, 156, and 157,
with fluor-spar and quartz ; and in Xo. 160 with francolite, a
variety of apatite. Copper-pyrites also occurs, rather exceptionally,
with boro-silicates like tourmaline and axinite, as at the Belstone
mines, in Devonshire, whence was obtained the specimen Xo. 151),
which exhibits the interesting association of chalcopyrite witli
garnet and axinite. f

Chalcocite. {Xos. 165 to 192.)

Xext to chalcopyrite, copper glance is the most abundant ore of
copper. This is a native cuprous sulphide, known to mineralogists
under a variety of names, such as Chalcocite, Redrutlute, and vitreous
copper ore. It occurs usually in the upper part of the lodes, above
the copper-pyrites, though in some cases the two sulphides are inter-
mingled. Probably much of the chalcocite may be regarded as a
secondary sulphide, produced by the alteration of copper-pyrites.

A large series of Cornish specimens of chalcocite, exceptional for
their beauty, is exhibited in this Case. The mineral crystallises in
the orthorhombic system, and some typical examples illustrating its
prismatic habit are here shown (Xos. 170, 171). The name redruth-
ite, sometimes appbed to this species, recalls the fact that many of the
finest crystals have been brought to light from mines in the neigh-
bourhood of Redruth. In many cases the crystals assume a hexa-
gonal habit which led some of the early mineralogists to refer the
species to the hexagODal system. Many fine examples of these
pseudo-hexagonal crystals, principally from St. Ives, will be recog-
nised here, notably Xos. 172 to 175. Twin crystals and triplets are
not infrequent, giving rise to star-shaped structures. It is easy to
understand from the shape of some of the crystals how the miners
have been led to call them " nail-headed copper ore."

Chalcocite is usually of a dark lead-grey colour, but many of the
crystals when fresh present a brilliant steel-grey appearance. On
exposure, the mineral is apt to suffer alteration, and acquire a dull

* " Lehrbuch der Mineralogie." Von Dr. Gustav Tsehermak, 4 Auf.,
1894, p. 354.

f " Notes on Minerals from Cornwall an'l Devon." Py R. II. Solly,
M.A., F.G.S. Min. Mag., vol. vi. (1886), p. 202.

38 MINERALS OF CORNWALL AND DEVON.

black surface. In other cases the surface becomes encrusted with
the blue copper sulphide, called covellite. It may also become
coated, under the influence of meteoric agencies, with copper
carbonates and other epigenic minerals, as is illustrated by No.
189 — a beautiful specimen of copper glance in which malachite is
creeping over the crystals.

Chalcocite is remarkably soft, sectile and fusible — so soft as to be
readily cut with a knife, like a piece of horn, and so fusible as to
melt in the flame of a candle. When massive as an ore it is some-
times called " black copper ore " and " grey copper ; " but these
names are ambiguous, inasmuch as the former is applied also to the
oxide called melanconite, and the latter to fahlerz or tetrahedrite.
Some forms of chalcocite are pulverulent and sooty.

Copper glance usually, though not invariably, occurs near the out-
crop of an ore-deposit, and gives way in depth to the yellow and
purple ores. Pseudomorphs of chalcocite after chalcopyrite are
known, and von Jeremeeff described their occurrence in quartz veins
near Georgeiff, in the Altai, where every stage from copper-pyrites
to copper glance may be traced.* It should be noted, however, that
the converse change likewise occurs, pseudomorphs being known in
which copper-pyrites has replaced copper glance.

Chalcocite may be produced by the reaction of sulphate of copper
on copper-pyrites or even on iron-pyrites. It is known as a pseudo-
morph replacing organic structures, and some specimens of wood
mineralised with chalcocite are shown in the Case of specimens
illustrating Fossilisation.

Roman bronze coins, and other objects containing copper, after
exposure to the prolonged action of certain thermal waters, have
yielded crystallised chalcocite. Some of Daubree's well known
examples from Bourbonne-les-Bains exhibited crystals of cuprous
sulphide which strongly reminded the mineralogist of the natural
crystals of Redruth, on a small scale.

Covellite. (Nos. 191, 192.)

Whilst cuprous sulphide constitutes the mineral described above
as chalcocite or copper glance, the cupric sulphide (CuS) also occurs
native and forms a mineral known as Covellite. This name was given
to it as a compliment to Covelli, an Italian mineralogist who showed
that cupric sulphide occurs among the erupted products of Vesuvius.
It is easy to understand how such a substance may be formed, by
the reaction of sulphuretted hydrogen on cupric chloride, which is a
volatile body found among certain volcanic exhalations.

Whilst the Vesuvian covellite is crystallised in forms belonging to
the hexagonal system, the covellite in copper- veins is usually found
as a blue incrustation on other copper sulphides, from which it has
evidently been derived. It is not uncommon as an alteration-pro-
duct on chalcocite, chalcopyrite and erubescite ; witness such

* Zeit. j. Kry.il., vol. xxxi. (1899), p. 508.

ERUBESCITE. .'J9

specimens as are shown here. By Breithaupt it was called Kwpfer-
indig, or indigo copper, since it bears some resemblance to indigo not
only in colour but in general appearance.

It has been shown experimentally by A. Knop that covellite may
be formed by the action of hydrochloric acid on copper glance or on
purple copper-ore— in the former case rapidly, in the latter slowly.
Some of the copper is removed as chloride, and the cuprous sulphide
(Cu : ,S) by this loss of copper passes into the condition of cupric
sulphide (CuS).*

Hochstetter recorded the occurrence of covellite as a thick dark
blue incrustation on an axe-head of bronze and on metallic copper
from a prehistoric site near Hallstatt, in Austria.t

Erubescite. (Xos. 193 to 204.)

Cornwall is remarkable, among mineral localities, for its fine
crystals of chalcocite already described, and not less for its crystals
of Erubescite. These crystals have been obtained chiefly from the
mines of Cam Brea, Tincroft, and Cook's Kitchen — three typical
localities near Redruth.

Erubescite crystallises in the cubic system, and many of the
specimens here exhibited show characteristic forms, such as inter-
penetrating cubes. It will be noted that some of the faces are slightly
curved, and in many cases the crystals instead of being distinctly
developed are confusedly aggregated, whilst in some cases the groups
of crystals take a marked linear extension.

\\ hen freshly fractured the mineral presents a bronzy or coppery
appearance, but it rapidl} suffers tarnish, especially in moist air, and
frequently becomes iridescent. The name erubescite, given by
Dana, is suggestive of the reddish tint which the mineral sometimes
assumes. In most cases, however, the superficial colour tends
towards purple, probably due to the formation of covellite, whence
the common name purple copper-ore. The tarnished surface is often
vivid in lustre and varied in tint — so varied that the German miners
call it Buntkupfererz, or variegated copper-ore. In consequence of
the bluish red appearance of the mineral, the Cornish miner com-
monly terms it horse flesh ore.

Erubescite was regarded by the early mineralogists as a form of
copper- pyrites, and it was not definitely separated from this species
until its crystalline characters and chemical composition came to be
understood. William Phillips first showed that the mineral was
cubic, and in his honour Beudant named it Phillipsite, a name which
is unfortunately ambiguous, since it is applied also to a certain
zeolitic mineral. Among the many designations of this copper-ore is
included the name Bornite, applied to it in compliment to Ignatius
von Born, a mineralogist who had charge of the mineral collection in
Vienna in the latter part of the eighteenth century. This name,

* Xeues Jahrbuch, 1861, p. o3Ij.

t Sitzungsber. Ak. Wise. Witn. Bd. Ixxii., Abth. I. (1879), p. 122.

-10 MINERALS OF CORNWALL AND DEVON.

given as far back as 1845, seems in truth to have priority over
Dana's erube cite, but the word bornite is apt to be confused by
rr.iners with bournonite.

Purple copper-ore is generally regarded as a double sulphide of
copper and iron, chemically akin to yellow copper-ore. Pure speci-
mens conform to the formula Cu 3 Fe S 3 , but the massive ore exhibits
considerable variation in composition, probably due to mechanical
mixture with copper glance or with copper-pyrites. According to
Rammelsberg, erubescite maybe viewed as a combination, in varying
proportions, of the three sulphides — Cu 2 S and On S and Fe S.
Groth's view regards it as a sulpho-ferrite of copper, derived from the
normal sulpho-acid Fe (SH) 3 by replacement of its hydrogen by
copper : Fe (S Cu) 3 .

The specimen No. 204 is notable for showing the erubescite in the
Win of lenticular chalcocite, and in association with calcite. The
pseudomorphs after chalcocite suggest one way in which it may have
been formed. It is probable, however, that in many cases it has
resulted from the alteration of copper-pyrites, and perhaps even of
iron-pyrites, by the action of waters containing copper sulphate.

Illustrations of the neogenic formation of erubescite are furnished
by the Roman coins and other bronze objects, which were thrown
as votive offerings into certain thermal springs, as at the famous
waters of Bourbonne-les-Bains, described long ago by Daubree.
After exposure to the action of these waters for some sixteen
centuries, the metal objects have become partially converted into
various copper-bearing sulphides, such as chalcocite, chalcopyrite and
erubescite. The subject will be referred to again, in connection with
the mineral called tetrahedrite, which has also been formed, and is
perhaps the most interesting of all these epigenic formations.

DIVISION 2.
MINERALS OF CORNWALL AND DEVON.

COPPER-BEARING MINERALS OF THE GoZZANS.

(Nos. 205 to 272.;

In a mineral- vein which carries pyrites in any form, it is usual to
find that the upper part of the deposit contains much brown oxide
of iron, or ferric hydrate. This rusty ore has resulted from the
alteration of the pyritic constituent of the lode under the influence of
oxidising agencies, and is therefore practically confined to the zone
of weathering. It usually marks the " back " or outcrop of the lode.
A tin -lode fairly free from pyrites is not likely to carry a ferruginous
capping of great extent, but most tin-lodes contain more or less
iron pyrites or mispickel, which may yield on decomposition hydrated
oxide of iron. In copper-lodes, however, this ferruginous mass is

GOZZAXS. 41

usually present in conspicuous amount, the iron of the copper-pyrites
yielding the brown hydrate ; and its characteristics are held Ijv ex-
po i ienced miners to bear some relation to the nature of the underlying
ore-body. The oxide of iron is generally associated with much of the
'jiiartzose veinstone, which is apt to present a cavernous or honey-
combed aspect, due to removal of the pyritic minerals.

This cellular mass of ferruginous matter is known in Cornwall as
gozzan, in France as the chapeau de jer, and in Germany as the eiseiner
Hut. The connection between gozzan above and ore below has been
regarded as so well established that it has given rise among German
miners to an old adage, which has appeared in several English
variants :

'' A Lode that wears no iron hat.
Is never likely to be fat."

Since the formation of the gozzan is generally due to the alteration
of pyrites, or in some cases to the alteration of carbonate of iron, it
may be assumed that it will be found only in the shallow part of a
mine, in the upper zone above the water level of the country, or in
what the late Prof. Posepny termed the vadose region. * Below the
plane of saturation, whither the influences that effect oxidation fail to
penetrate, the metallic sulphides may retain their original character
with but little alteration. It may happen, however, that these
agencies, operating along deep fissures, make themselves felt at con-
siderable depths. Thus in Cornwall the gozzan has extended to as
great a depth as 100 fathoms below the adit level at Fowey Consols :
in Ting Tang Mine the gozzan went down to 150 fathoms ; whilst
at Dolcoath oxidised products have been found as deep as the 197
fathom level. |

In the weathering of iron-pyrites the sulphide is oxidised to the
condition of ferrous sulphate, with formation of free sulphuric
acid. This sulphate, perhaps after passing to the condition of ferric
sulphate, is ultimately converted into ferric hydrate, or, as it is
sometimes called, hydrate of iron. The reactions in the oxidation
and hydration of pyrites have been studied by Mr. W. H. Weed
and by Mr. R. A. F. Penrose, j

It is probable that the alteration of pyrites to limonite is often
effected through the intermediate formation of ferrous carbonate, a
rather unstable compound easily decomposed in the presence of
air and water, with production of ferric hydrate. Dr. J. W.
Evans has called attention to the action of carbonates in promoting
the limonitisation of pyrites. His experiments showed that metallic
sulphides exposed to water free from carbonates are usually con-
verted into sulphates, but that the presence of carbonates determined

* On the circulation of subterranean water, see Prof, van Hise's papers :
" Principles controlling the Deposition of Ores." Journ. Gaol., vol. viii.
(1900), p. 730. Trans. Am. Inst. Min. Eng., vol. xxx. (1901), p. 27.

f On Cornish Gozzan, often s;.elt Gossan, see W. Argall in Rep. Min.
Assoc, 1872, p. 37. Also J. H. Collins in Journ. R. Inst. Corn., vol. ix., p. 471.

% Journal of Geology, voL ii. (1894), p. 288.

42 MINERALS OF CORNWALL AND DE\ ON .

the formation of oxides, hydrates and carbonates. In the case
of iron-pyrites, the first product of alteration in the presence of
carbonates is usually the hydrated oxide.*

The specimen No. 205 is a sample of gozzan from a copper-lode
at Devon Great Consols. A large series of examples will be found
among the vein-stones in Wall-case 35. They are not showy speci-
mens, but are of much significance to the miner, since the character
of the gozzan usually bears some relation to that of the ore-body,
though sometimes it happens that a rich gozzan may cap a lean lode.

To the mineralogist the gozzany part of a vein is often of supreme
interest, for many of the finely crystallised specimens of oxides,
carbonates, phosphates, arsenates and other oxysalts, have had their
birthplace in the region of the gozzan. An extensive series of such
specimens, including many of great beauty, is exhibited in the
Case under description and in some of the succeeding Cases.

Cuprite. {Nos. 206 to 226.)

Two oxides of copper occur in a native condition — the red or
cuprous oxide (Cu 2 0) an< i the black or cwpric oxide (CuO), forming
the minerals known respectively as cuprite and melaconite. In the
mines of Cornwall and Devon these copper oxides have
usually been derived from the alteration of copper sulphides.

Cuprite, or red copper ore, not unfrequently occurs in sharply
defined crystals, of the cubic system, rich in colour and brilliant in
lustre. The crystals, as shown here, are usually octahedra, or less
commonly cubes and rhombic dodecahedra. Some of the specimens
(such as Nos. 210, 214, 215) present a colour, lustre and translucency
which justify the name of ruby copper ore, sometimes applied to this
specios. As the mineral is apt to become dull and opaque by pro-
longed exposure to light the finest specimens are not exhibited in this
Case. Wheal Phoenix, near Liskeard, yielded at one time crystals
of cuprite, which in beauty and brilliancy rivalled gem stones ; and
many of these specimens are preserved in japanned tin cases in the
Ludlam cabinets, where they may be seen by students, on application
to the curator.

A remarkable variety of cuprite is furnished by the capillary
forms known as Chalcotrichite or plush copper (Nos. 225, 226). These
delicate filaments, of carmine colour and silky lustre, are acicular
crystals, the system of which was formerly a matter of dispute ; but
they are now known to be cubes greatly elongated, usually in the
direction of a diagonal.

In many of the specimens, such as Nos. 206 and 207, the associa-
tion of cuprite with limonite reveals its origin from copper-pyrites,
the sulphides of the two metals, copper and iron, being here repre-
sented by the oxides. An intimate mixture of cuprite and limonite
is sometimes found as an earthy substance, brick red or reddish
brown in colour, and is known to miners as tile ore.

* " The Alteration of Pyrite by Underground Water." By John W.
Evans, LL.B., D.Sc. Min. Mag., vol. xii. (1900), p. 371.

CUPRITE AND MELACONITE. 4-')

At the beginning of the nineteenth century, great discoveries of red
copper-ore were made in Cornwall, where it had previously been a
very rare mineral. Mr. W. Phillips described and figured the fine
crystals from Wheal Gorland, near St. Day in Gwennap.* Here
there were three lodes, but most of the cuprite was yielded by the
gozzany part of the Muttrell Lode, " one to which no other lode
hitherto discovered in the county of Cornwall bears any analogy."
The gozzan extended to a considerable depth, and yielded a great
deposit of cuprite, associated with native copper, copper glance,
black oxide and arsenate of copper, mispickel, quartz and fluorspar.
It is believed that many of the specimens of cuprite here exhibited
were obtained from this deposit.

Cuprite is not unfrequently found in a crystalline condition on
ancient objects of copper or bronze, which have lain long in damp
ground. Bronze celts sometimes show this alteration. The surface
of the object is coated with green carbonate of copper, beneath
which is a crust of red oxide, enveloping a nucleus of the original
alloy. In certain cases bronze coins show a similar change. Mr.
L. Fletcher has described an interesting case of the occurrence of
piles of Roman coins at Chester, which had been buried for fifteen
centuries, where the cavities between the piles were lined with
crystals of red oxide and with blue and green carbonates of copper,
associated with yellow carbonate of lead.f Professor Lacroix has
described in like manner the alteration of old Roman coins from
Algeria, where the metal has yielded cuprite, malachite and cerus-
site.J In the thermal waters of Bourbonne-les-Bains, and at some
other localities, crystals of cuprite have been found on some of the
bronze objects which have been exposed for centuries to the action
of the waters.

The artificial production of cuprite was effected by Mitscherlich,
by the slow reduction of a solution of copper sulphate through the
agency of organic matter. It is believed that a similar de-oxidation
may be effected by means of ferrous compounds, and a simple ex-
planation is thus afforded of the possible formation, in certain cases,
of the natural oxide.

Melaconite. {Nos. 227, 228.)

Cupric oxide in its native condition is known as Melaconite, and
occurs usually as a dull earthy pulverulent substance, coating other
copper-ores from which it may have been derived. In Xo. 228 it
encrusts chalcosite. Crystals are extremely rare, and the crystal-
lised specimen No. 227 is interesting as having been obtained from

* " A Description of the Red Oxyd of Copper, the Production of Cornwall
and of the Varieties in the form of its Crystal, with Observations on the Lodes
which principally produced it ; and on the Crystallization of the arseniated
Iron." By William Phillips. Trans. Geolog. Soc, vol. i. (1811), p. 23.
i j- " On Crystals of Cuprite and Cerussite resulting from the slow alteration
of Buried Coins." By L. Fletcher, M.A. Min. Mag., vol. vii. (1887), p. 187.

+ Bull. Soc. Min. Fr., tome vi. (1883), p. 175.

x ^ ' ■ ■ • -=■•-

44 MINERALS OF CORNWALL AND DE^ON.

Mr. Tailing, and being the counterpart of the material studied by
Prof. Maskelyne, who described the crystals forty years ago.*
They belong to the monoclinic system. These crystals were
analysed by Professor Church, who was the first to call attention to
their occurrence. "j"

The substance termed black copper ore, which occurs in the gozzan
of many copper lodes, is a more or less impure form of melaconite.
This black ore was known to old Cornish miners as poder — a word
which De la Beche suggests may be a corruption of the word
" powder," applied to the ore in consequence of its pulverulent
character.! The value of this substance, so unattractive to the eye,
was for a long time ill understood, and according to Pryce a quantity
representing several thousand pounds in value was washed into the
sea from Old Pool Mine.

Crystalline scales of cupric oxide occur on Vesuvian lavas, and are
known mineralogically as Tenorite. There they are no doubt
formed by sublimation, whilst in copper-lodes the mineral results
from the alteration of copper-ores, such as chalcosite, with which it
is often associated.

Native Copper. (Nos. 229 to 244.)

Native copper, known to miners as virgin copper or malleable copper,
occurs to a greater or less extent in almost all the copper mines of
Cornwall. It is usually found in the upper or gozzany part of the
lode, where it has evidently been formed as a secondary product by
the reduction of certain cupriferous compounds. Rarely, if ever,
. in well denned crystals, it often assumes dendritic and arborescent
forms, spreading out in picturesque branches, or expanding in thin
laminae, or shooting out in delicate filaments like moss. Some of the
branches are aggregates of small distorted crystals. The character-
istic association of native copper with cuprite is illustrated by Nos.
221-224.

Copper is reduced with such facility from solutions of its salts,
especially the sulphate, that the formation of native copper presents
no difficulty. In old mine workings, metallic copper may be readily
precipitated from cupreous waters by means of metallic iron ; and
in this way such objects as iron chains, bolts and nails will readily
throw down cement copper. Decomposing organic matter is also an
agent of reduction, and hence decaying wood frequently determines
the local precipitation of the metal. Mr. W. H. Baker has described
the occurrence of crystals of native copper on mine timber at the
Kawan Mine, in New Zealand, found on re- opening the workings
after they had been closed for twenty years. Some instructive
examples of metallic copper formed around wood and iron objects,
in old mines, will be found in Wall-case 35.

* " On Crystals of Melaconite, and on Tenorite." By Prof. Maskcljne,
M.A. Brit. Assoc. Rep., 1865, p. 33.
f Gh'em. News, Mar. 17, 1865. p. 122.
X Rep. Oeol. Cornwall, p. 591.

NATIVE COPPER, ETC. 45

Native copper may also be reduced from cupreous solutions by
natural electrolytic action, or by the influence of deoxidising media,
like metallic sulphides, or even magnetite. Probably ferrous sul-
phate has been in many cases the reducing agent. It has been
shown that the conditions under which ferrous salts may be oxidised
with deposition of metallic copper are precisely those which obtain
in the circulation of underground waters.*

Pseudomorphs of native copper having the form of octahedral
crystals of cuprite are well known. The copper is in a spongy con-
dition, through loss of matter, and has probably been formed by the
action of weak sulphuric acid, which would give rise to cupric sul-
phate and free copper.f A similar reaction may have been respon-
sible for the origin of large masses of native copper.

On the contrary, native copper may give rise to cuprite and other
oxidised compounds, by exposure to meteoric influences. Metallic
copper, in its natural condition is, however, very slowly affected by
oxidising agencies.

The specimen No. 248 shows native copper embedded in the
serpentine of the Lizard district, in south-western Cornwall.

In the Hall of the Museum are some very large masses of native
copper from a mine at the Ghostcroft, Mullion, where it occurred near
the junction of the serpentine with hornblende schist. These were
exhibited, with some still larger specimens, in the Great Exhibition
of 1851.*

In the well-known copper-deposits of Monte Catini, near Florence,
the ore occurs in connection with masses of serpentine and gabbro.
The commonest mineral is copper-pyrites, but this in some parts
passes superficially into erubescite, chalcosite and native copper.
The Tuscan serpentine has been regarded as an altered cupriferous
peridotite. According to B. Lotti§ the ores may have resulted from
the differentiation of a strongly basic eruptive magma, rich in mag-
nesium — a view supported by Vogt.jl

Copper is a metal much more widely distributed in nature than tin.
Its ores occur not only in igneous rocks of acid type, like those
which carry tin ore, but also — and perhaps more frequently — in basic
eruptive rocks.

Malachite and Chessylile. (Nos. 245 to 252.)
Any body of copper-ore, on exposure to meteoric activities, is apt
to become more or less altered to the condition of carbonate. The

* "' The Deposition of Copper by solutions of Ferrous .Salts." By H. C.
Biddle. Journ. Geol. (Chicago), vol. ix. (1901), p. 430.

f Cu 2 + H 2 S0 4 = Cu + CuS0 4 + H,0. With respect to precipitation in the
zone of weathering, see W. H. Weed : " The Enrichment of Gold and Silver
Veins." Trans. Aincr. Itiit. Min. Eng., vol. xxx. (1901), p. 42(.

j On the Lizard copper, see F. J. Stephens. Trans. R. Geol. Svc. Curn.,
vol. xi. (1895), p. 680.

5 " Sulla genesi del giacimenti metalliferi nelle roccie eruttive basiche."
— Boll. d. R. Com. Geolog. d" Italia, vol. xxiv. (1893), p. 343.

] " Beitrage zur genetischen Classificationen der durch magmatiache
Differentiationsprocesse und den durch Pneumatolyse cntstandenen Erzvor-
kommen."— Ze.it. f. prakt. Geol., Oct. 1894, p. 381.

46 MINERALS OF CORNWALL AND DEVON.

brilliant colours of the carbonates of copper render them conspicuous
on the back of the lode. Specimens are here shown of the green
carbonate or Malachite (Nos. 246 to 248) and of the blue carbonate
or Chessylite, known also from its colour, as Azurite (Nos. 250-252).
These related minerals are often associated, as in No. 250. The
Cornish specimens usually occur as encrustations, sometimes fibrous
but rarely crystallised. The delicate green fibrous malachite in No.
248 comes from South Caradon, near Liskeard. The crystals on No.
251 show chessylite in a pseudomorphous form, replacing crystals of
the arsenate called clinoclase.

The recent formation of carbonate of copper is illustrated by No.
245, which is a sample of a material raised at one time as an ore at
Wheal Leisure, near Perranzabuloe. This consists of grains of sand,
with pebbles and recent shells, cemented by copper-ore, chiefly green
carbonate, which is known to have been formed in the course of
fifteen years by the action of rain-water percolating through the
waste heaps of an old mine. This specimen was presented, with
others, by the late Sir Warington Smyth, F.R.S.

Of a somewhat similar character is the specimen, No. 246, re-
cently obtained by Mr. J. B. Hill, of the Geological Survey, in
which green carbonate of copper of recent formation is associated
with shelly sand from Carbis Bay.

Malachite and chessylite are usually described as hydrated carbon-
ates, but as the water is not expelled until the minerals are exposed
to a high temperature it may be assumed that the water is consti-
tutional, the hydroxyl acting as a base ; hence the minerals are
really basic carbonates.

ChrysocoUa. (Nos. 253, 254.)

Copper may appear as a silicate wherever copper ores are exposed
to the action of siliceous solutions. The copper silicate known as
ChrysocoUa presents a bluish green colour, with an opaline lustre,
and is usually found in botryoidal or encrusting masses. The speci-
mens here shown are well-defined crystals of cuprite, converted
superficially into chrysocolla, with retention of perfect form.
ChrysocoUa seems in all cases to be an amorphous product of the
alteration of other copper ores, and the form presented by these
specimens is of course pseudomorphous.

Chalcanthite. [Nos. 255, 256.)

Although sulphate of copper must be a very common product of
the oxidation of copper sulphides, its ready solubility in water
renders it unfit to survive, as a mineral, amid the damp surround-
ings of a mine. It is, therefore, only under rather exceptional con-
ditions that the solid salt is found in nature. As a mineral, the
cupric sulphate is known as Chalcanthite or cyariosite. The specimens
here exhibited show the beautiful blue colour which has led to the
common name blue vitriol. In one of the specimens the salt exhibits

LANGITE, WOODWARDITE, ETC. 47

a fibrous structure, whilst another shows the mineral in small
sharply- defined anorthic crystals, seated on killas. The burrows, or
heaps of old mine -refuse occasionally contain chalcanthite.

A solution of sulphate of copper draining through a mineral vein
furnishes a ready means for migration of the copper. It is probable
that such cupreous solutions, descending to lower levels, may effect
the secondary enrichment of many copper lodes by furnishing
material from which copper sulphides may be precipitated, as pointed
out by Mr. S. F. Emmons and Mr. W. H. Weed in the papers
already cited (p. 35 >.

Langite, Woodwardite, etc. {Nos. 257 to 266.)

The beautiful mineral Langite is a basic cupric sulphate, described
in 1*04 by Prof. X. S. Maskelyne, who detected it on specimens sent
to the British Museum by the late Mr. Tailing.* It occurs on killas
and on a quartzose veinstone, in the form of minute blue crystals
belonging to the orthorhombic system : it is found also as an in-
crustation and as a cementing medium in a breccia of killas. Mr.
Collins gives its localities as Copper Hill Mine and Wheal Bassett,
Redruth ; and East Pool, Dolcoath and other mines near Cam-
borne, f

Langite was so named by Prof. Maskelyne in compliment to Prof.
Viktor von Lang, of Vienna, who was at one time an officer in the
mineralogical department of the British Museum. Lyellite is
Maskelyne's name for a somewhat similar mineral, which Pisani
called DeviUine (No. 262)4

It was pointed out by Maskelyne and Flight that solutions of
sulphate of lime or magnesia reacting on malachite might give rise
to a basic cupric sulphate like langite. §

Closely associated with langite is another mineral which Prof.
Maskelyne described at the same time under the name of Waring-
tonite — a name given in honour of the late Sir Warington W. Smyth,
who was for many years lecturer on mineralogy and mining at the
Royal School of Mines, and in that capacity had charge of the mineral
collections in this Museum (b. 1817, d. 1890).

Under the name of Woodwardite Professor Church described, in
1866, a Cornish mineral which he found to be a hydrated cupric-
aluminium sulphate. || The specimen shown here presents the
mineral in the form of a thin crust having a peculiarly rippled

* " A new British Mineral." —Phil. Mag., vol. xxvii. (1864), p. 310.

■f " A Handbook to the Mineralogy of Cornwall and Devon," 1*71, p. Gl.

X Comptes Bendus, vol. lix.(1864), p. 813.

§ Journ. Chem. Soc., [2] vol. ix. (1871), p. 2. Chemical News, vol. xxii.,
(1870) p. 259.

I " Chemical Researches on New and Rare Cornish Minerals, iv. A New
Hydrated Cuprie- aluminum Sulphate." Journ. Chem. Soc, [2] vol. iv. (1S66),
p. 130.

48 MINERALS OF CORNWALL AND DEVON.

surface and a beautiful turquoise blue colour. The name was given
in memory of Dr. S. P. Woodward, of the British Museum, the
author of the well-known " Manual of the Mollusca " (b. 1821,
d. 1865). The mineral has close relations to langite.

No. 265 is a specimen of a stalagmitic mineral of recent formation,
found by Sir C. Le Neve Foster at St. Agaei, and described as
Enysite by Mr. J. H. Collins, who found it to be a basic sulphate of
copper and aluminium.*

Conndlite. (Nos. 267, 268.)

r The extremely rare mineral Conndlite is a hydrous sulphato-
chloride of copper, which was first examined chemically by Prof.
Connell.f after whom it was named by Dana. It occurs in delicate
diverging fibres, of a fine Prussian blue colour, belonging to the
hexagonal system. The crystallographic characters of the species
have been described by Prof. Maskelyne, and the chemical by Prof.
Penfield.|

No. 268 is the specimen referred to by Greg and Lettsom, when
they say : " In Mr. Turner's collection there is a specimen stated in
the catalogue to be from Carharrack in St. Day." § In Levy's
catalogue of 1837 it is described as cuivre vdoute, without any
reference to its composition.! | The mineral is associated in this
specimen with cuprite and a little mispickel, on a matrix of quartz.

In the catalogue of the Eashleigh collection — a collection recently
acquired by the Royal Institute of Cornwall, through the generosity
of Mr. Bnys and others, and now exhibited in the museum at Truro —
there is a figure of connellite, described as " copper ore of an azure
blue colour composed of needle crystals. "|f

About twenty years ago the mineral was found in the Camborne
district and in Marke Valley, and its occurrence was described by
Mr. W. Semmons.** It occurred in copper veins traversing killas, and
was associated with cuprite, malachite, brochantite, etc. The crystals
were described by Prof. Miersfj and by Dr. C. 0. Trechmann.J|

The somewhat similar mineral, termed by Prof.Penfield Spangolite,
has been detected on Cornish specimens by Prof. Miers.§§

* Min. Mag., vol. i. (1877), p. 14.

f " Oq Sulphato-chluride ot Copper — anew mineral." — Brit. Assoc. Rep.,
1847, part ii., p. 49.

% " On Connellite from Cornwall, England." Amer. Journ. Sc, [3] vol xl.
(1890), p. 82.

§ Manual of the Mineralogy of Great Britain, etc., p. 347.

|| Vol. iii., p. 100, No. 4.

*|| " (Specimens of British Minerals sclcHcd from the Cabinet uf Philip
Kashloigh." Part ii , 1802, p. VI. PI. xii., tig. 1.

** " Motes on a recent Discovery of Connellite." By W. Semmons. Min.
Mag., vol. vi. (1886), p. 160.

ft Ibid., p. 167.

1% Ibid., p. 171.

§§,,•< Spancolite.'' By H. A. Miors, M.A. Min. Mag. vol. x. (1834),
p. 273.

ATACAMITE. i'.l

Atacamite, tie. (\os. 269 to 272.)

In certain parts of the world the chlorides of copper have played
at times an important part in the production of copper, but in Corn-
wall they occur only as great rarities. Atacamite, the oxychloride,
which is the best known member of the group, finds no place among
the British minerals described in Greg and Lettsom's standard work.
Indeed, it was not recognised as a British species until recorded by
Prof. Church in 180-~>.

The specimens show the mineral in minute crystals (No. 270), as an
incrustation and in the form of tubular stalactites (Xo. 269).
In some places atacamite may have been formed by the action of
salt-water on oxides of copper, as pointed out by Mr. Cloud with
reference to the famous occurrence at Wallaroo in South Australia.*
The specimens here shown are from Botallack Mine, close to the sea ;
but chlorides may also be formed inland, since rain water usually
contains more or less salt.

The infiltration of sea-water into a part of Botallack Mine was no
doubt responsible for the formation of the cupric oxychloride which
Prof. Church described as Botattackite, of which a specimen is seen
inXo. 271-t

Tallingite (Xo. 272) is another mineral closely related to atacamite
described by Prof. Church.* The name recalls the services of an
observant collector, the late Mr. R. Tailing, who brought to light
several new minerals from the West of England, and from whom a
large number of the specimens here exhibited were originally
obtained.

* " Note on Atacamite-."' By T. C. Cloud, A.R.S.M. Chan. Sews, vol.
xxxiv. (1870;, p. 2ol.

t " Notes on a Cornish Mineral of the Atacamite Group." Journ. Chem.
Hoc. [2), vol. iii. (180.5), p. 212.

% " On some Hydrated Cupric Oxychlorides from Cornwall." Journ.
Chem. Hoc. [2], vol. iii. (1865), p. 77.

7882.

oO MINERALS OF CORNWALL AND DEVON.

CASE III.

DIVISION 1.
MINERALS OF CORNWALL AND DEVON.

Arsenates and Phosphates from the Copper Gozzans.
(Nos. 273 to 340.)

The series of secondary minerals found in the gozzans of the
copper lodes is continued in this Case by an extensive group of the
arsenates and phosphates of copper. Many of the old mines of
Cornwall were famous for these minerals, and the beautiful speci-
mens here exhibited fully justify their reputation. Other examples
as fine, or even finer, will be found in that part of the Ludlam collec-
tion which is exhibited in the Hall.

In the Cornish veinstones, arsenic seems to be more common than
phosphorus, and it will consequently be observed that in this Case
the arsenates form a grander show than the phosphates. The
arsenic seems to have been originally brought up, in association
with iron and sulphur, as arsenical pyrites. The species called
misfickd has already been noticed (p. 31) and will again be referred
to in connection with pyrites (p. 62). Mispickel contains theoreti-
cally nearly half its weight of arsenic ; but even in ordinary pyrites,
arsenic may be present in small proportion. The alteration which
arsenical pyrites suffers in the oxidation-zone of a vein has no doubt
furnished material for the formation of various arsenates. The
mine-waters in Cornwall are known to be frequently arsenical.

The original source of the phosphorus in the phosphatic minerals
of the veinstone is perhaps not quite so obvious. It has, however,
been probably derived, directly or indirectly, from apatite. This
mineral, as already remarked (p. 24), is widely distributed in eruptive
rocks, both acid and basic, but especially the latter. At a very early
stage in the consolidation of the magma, the phosphorus separated
as calcium phosphate, and the minerals which subsequently crystal-
lised had to mould themselves around the pre-existing crystals of
apatite. Hence the apatite usually appears as inclusions enveloped
in the other rock constituents.

It is true that in some cases, the apatite appears to offer much
resistance to agents of alteration, and its crystals may remain fresh
even when the surrounding matter has suffered more or less decompo-
sition. But, on the other hand, apatite is known to be readily
attacked by acids, even by water containing carbonic acid, and it has
undoubtedly furnished phosphatic matter to the circulating waters,
which would help to form metallic phosphates in the vein. Sulphuric

OLIVENITE, LIBETHENITE, ETC. 51

acid, from decomposing pyrites in a vein, will readily attack apatite.
Again, all surface water contains more or less calcium phosphate,
probably derived, for the most part, from organic sources ; and,
hence, surface drainage may carry phosphates into the shallow parts
of a lode, and so give rise to reactions resulting in the formation of
secondary phosphates as minerals of the gozzan.

The chemical composition of the arsenates and phosphates has
been the subject of prolonged researches by Prof. A. H. Church* ;
and the subject has been taken up in recent years by Mr. G. J.
Hartley. t

Olivenite, Libethenite, etc. (Nos. 273 to 302.)

It will be seen from the rather large series of specimens of olivenite
(Nos. 27:i to 29<J) that the olive green colour, which led Werner to
name the species, is subject to much variation. Nos. 273 and 274
show brilliant crystals, belonging to the orthorhombic system,
seated on brown iron- ore, so as to show their relation to the gozzan,
and presenting a very dark green colour, inclining to black. Wood
copper, or wood arsenate, is the name applied to the fibrous varieties,
which often appear in delicate filaments, with a silky lustre, fre-
quently of pale colour passing into ash grey or even white, and
sometimes disposed in masses which present a velvet-like surface.
Examples of the fibrous olivenite are exhibited in Nos. 290 to 296.

Most of the olivenite here shown, as well as some of the other
copper arsenates in this Case, came from Wheal Unity, in the parish
of Gwinear. Mr. W. Semmons has remarked that " Wheal Unity was
a perfect storehouse of copper minerals, no less than fourteen com-
binations of that metal being found there. "|

Olivenite is generally described as a hydrated arsenate, but the
water is probably represented by hydroxyl, and the mineral may,
therefore, be regarded as a basic arsenate of copper. Its formula,
Cu 1? (OH)As0 4 suggests its derivation from ortho-arsenic acid.§ The
series of arsenates and phosphates are isomorphousj|, and part of the
arsenic in olivenite is consequently replaced in many cases by
phosphorus, without disturbance of crystalline character. When
the replacement is complete, the resulting compound has the formula
Cu 2 (OH)P0 4 . This constitutes the mineral known as Libethenite —
a mineral which owes its name to a locality in Hungary. In Corn-
wall this phosphate is even more rare than olivenite. Specimens are
shown as Nos. 297 to 302. In some of these examples the libethenite
is crystallised on gozzany ironstone, and in others on malachite —
associations which in both cases recall the formation of the phosphate
as a secondary mineral.

* Journ. Chem. 8oc, various volumes from 1865.

| " On the Constitution of the Mineral Arsenates and Phosphates."
Min. Mag., vol. xii. (1900), pp. 120, 152, 223.

J Min. Mag., vol. vi., p. 160.

§ Sea Groth, op. cit., p. 89.

|| Iaomorphoui sub3tance3 are tho3e which pa339ss amlo*y of chemical
composition with close resemblance, or even identity of crystalline form.
7882. E 2

■ )1 MINERALS OF CORNWALL AND DEVON.

The rare phosphate of copper called Lunnite, or pseudo-malachite,
is represented by Nos. 301, 302. Specimens from Botallack were
analysed by Prof. Church.*

Clinoclase and Cornwallite. (Nos. 303 to 311).

Clinoclase is a basic copper arsenate corresponding among the
arsenates to pseudo-malachite among the phosphates. It occurs in
dark greenish-blue crystals, referable to the monoclinic system,
the name expressing the fact that the basal cleavage is inclined to
the faces of the oblique prism. No. 304 shows the mineral in the
form of a spherical mass, with curved cleavage-planes ; whilst Nos.
305 to 307 illustrate its characteristic occurrence in dark blue fibres
aggregated in diverging and stellate groups.

The very rare mineral, Cornwallite is a hydrated basic arsenate of
copper, occurring in small botryoidal masses. Its composition has
been determined by Prof. Church. f and the specimen here exhibited
as No. 309 is interesting as being a portion of the specimen which he
analysed. Other examples of cornwallite are shewn in Nos. 310, 31 1.

The Cornish arsenates of copper were studied in the beginning of
the last century by the Comte de Boumon, who was led to remark
that " Nature has established very remarkable differences between
the arseniates of copper."]: The justice of this remark will be
admitted by the visitor who, sweeping his eye over the minerals in
this Case, contrasts the superficial characters of such species as
olivenite, clinoclase, liroconite and chalcophyllite.

Liroconite. {Nos. 312 to 321.)

From all other copper arsenates the species termed liroconite is
usually distinguished by its beautiful sky-blue colour. The mineral
occurs in sharply defined crystals, belonging to the monoclinic
system, and the old name octahedral arseniate of copper was intended
to indicate their general shape. This species differs from the
arsenates previously noticed, inasmuch as it contains aluminium as
an essential constituent : it may be regarded in fact as a hydrated
basic arsenate of copper and aluminium. It seems to have been
found only in Wheals Unity, Gorland and Muttrell, in Gwennap ;
and, as some of the specimens here show, it was found with other
oxidised products in the gozzany part of the veinstone. Some
exceptional specimens of this species are included in the Rashleigh
collection now in the museum of the Royal Institution of Cornwall
at Truro.

* Joum. Chew. Soc. [2], vol. iii. (1865), p. 2.

t Joum. Chem. Soc, [2] vol. vi. (1868), p. 276.

% "Description of the Arseniates of Copper and of Iron, from the countv
of Cornwall." By the Count de Boumon. Phil. Trans., vol xei fisnif
- 169. ' K >'

CHALCOPHYLLITE, ETC. ■)■'>

Chalcophyllite. (Nos. 322 to 328.)

The rare and beautiful mineral called Chalcophyllite, known also as
Tamarite from its occurrence at Wheal Tamar, is represented by a
series of excellent specimens. It crystallises in the hexagonal
system, and the crystals usually assume a tabular habit, as well seen
in most of the examples here exhibited. The six-sided plates present
perfect basal cleavage, whence the name copper mica, sometimes
applied to this species. The shape and the fine emerald green colour
give the mineral in some cases a certain resemblance to " uranium
mica," or torbernite (p. 82).

Chalcophyllite has generally been regarded as a hydrated basic
arsenate of copper and aluminium, but the analysis of a Cornish
specimen, carefully separated from foreign matter, by Mr. E. G. J.
Hartley, has revealed the presence of a sulphate.*

Some of the specimens here exhibited show the chalcophyllite
associated with chalcopyrite, and others with decomposing mis-
pickel, thus betraying the origin of the mineral. In No. 328 the
substance seems partially altered to chrysocolla.

Bayldonite, etc. {Nos. 329-331.)

Under the name Bayldonite, in honour of Dr. John Bayldon, at
one time Professor in the Royal Agricultural College at Cirencester,
Prof. Church described, some forty years ago, a new species, which
occurs as a concretionary mineral of green colour, seen in Nos. 329
and 330, where it coats a gozzany quartzose veinstone. This species
is a hydrated basic arsenate of copper and lead.j

No. 331 is a specimen of Chenevixite, which is a hydrated basic
arsenate of copper and iron, occurring as a dull greenish amorphous
substance on a quartzose matrix.

Andrewsite, Chalcosiderite, etc. (Nos. 332 to 340.)

Andrewsite is a mineral described in 1871 by Prof. Maskelyne, and
named after the late Dr. T. Andrews of Belfast.^ It occurs in small
bluisr- -green globular masses, with a radiate structure, as shown in
No. 332. Sir C. Le Neve Foster described its occurrence at Wheal
Phoenix Mine, near Liskeard, where it is found in a tin-lode in
granite, carrying much limonite and a little copper glance and
cuprite, s

A bright green mineral occurring with the Andrewsite of Wheal
Phoenix was referred by Prof. Maskelyne to Ullmann's species

* " Communications from the Oxford Mineralogical Laboratory." Min.
Mag , voL xii. ( 1900), p. 120. See also Prof. Church in Journ. Chem. Soc. [2]
vol. ^ii. (1870), p. 168.

+ Journ. Chem. Soc. [2], vol. iii. (1865), p. 265.

% " On Andrewsite." Brit. Ass. Eept. for 1871, p. 75. Journ. Chem. Soc.
[2] vol. xiii. (1875), p. 586.

§ " On Andrewsite." Trans. R. Geol. Soc. Corn., vol. ix. (1875), p. 163.

54 MINERALS OF CORNWALL AND DEVON.

Chalcosiderite* It crystallises in the anorthic system, and the speci-
mens Nos. 333 to 336 show crystals seated on a gozzany matrix.
Both chalcosiderite and andrewsite are hydrated phosphates of iron
and copper. A trace of uranium has been found in chalcosiderite.
Henwoodite, from the same mine, is a mineral named by Mr.
J. H. Collins after Mr. W. Jory Henwood (b. 1805, d. 1875). It
occurred in small globular masses of a turquoise blue colour on
limonite, and seems to be a hydrous phosphate of copper and
aluminium. f Its characters are well seen in Nos. 337 to 340.

DIVISION 2.
MINERALS OF CORNWALL AND DEVON.
Ores of Lead, Zinc, Antimony, etc.
(Nos. 341 to 408.)

Whilst the tin- and copper-lodes of Cornwall and Devon generally
run in a direction which may be roughly set down as nearly E. and W.
or N.E. and S.W., those veins which carry lead often take a course
nearly at right angles to this direction. Such veins are therefore
known as " cross-courses." Many of these cross veins are quite
unproductive of ore, whilst others are richly plumbiferous. The
N. and S. veins are usually of later date than those which hold an
E. and W. course, as attested .by the fact that the former may in
some cases be seen to cut across and dislocate the latter. The intro-
duction of the lead-ore, probably by means of thermal waters, seems
to have been effected subsequently to the deposition of the minerals
of the tin-copper lodes. Lead-ore is not confined, however, to the
cross-courses, but is sometimes found in the veins which have a bearing
more or less approximately east and west. The ore of lead is not
infrequently associated with copper-ore, but very rarely indeed with
tin-ore. The typical lead-lodes are in killas, and in certain cases at a
considerable distance from granite ; some of the most productive
mines having been in the eastern and northern divisions of Cornwall
and the adjacent part of Devonshire, and some even in North Devon.
The ore is normally galena, or lead sulphide, and the matrix fre-
quently contains fluor-spar. At the present time but little lead-ore
is being raised in Cornwall and none in Devon ; and a similar remark
applies to zinc-ore, though some of the old burrows, or waste-heaps,
may be worked over for sake of the blende.

Ores of zinc frequently accompany those of lead. The zinc usually
occurs as sulphide, or zinc blende, and in Cornwall this mineral is
rather widely diffused, often in association with lead-ore and not
infrequently with copper-ore, though only occasionally with tin.

* "On Andrewsite and Chalkosiderite." Journ, Chem. Soc, [2] vol. xiii.
(1875), p. 586.

t Min. Mag., vol. i. (1877), p. 11.

LEAD-ORES. 55

Antimony has been yielded from time to time by manv Cornish
mines, especially in the northern part of the county, where the killas
is remote from granite, but associated in places with greenstone. Up
to a recent date small quantities were obtained from this district,
but at the present time none is being worked.

Galena, Cerussite, and Pyromorphite (Nos. 341 to 380).

In Cornwall and Devon, as in most other lead districts, the common
ore of lead is the sulphide, known as Galena, a mineral which crys-
tallises in the cubic system, and admits of perfect cubic cleavage.
Some excellent examples of crystallised galena are here exhibited,
the cubo-octahedra* of Xos. 343 and 346 being characteristic
crystals of this species. But as a larger series of specimens of
galena crystals will be found among the minerals from the lead
districts of the North of England (pp. 187, 162) no detailed notice is
needed in this place.

Many of the specimens here exhibited illustrate the paragenetic
relations of galena in the SAY. of England. Chalybite, or ferrouscar-
bonate, is a characteristic companion of galena, and the two minerals
may be seen together in Xos. 343 and 345 ; blende, or zinc sulphide,
is another common associate, as shown in Xo. 348 ; whilst pyrite, or
iron sulphide, is very widely distributed in the lead veins as in
the other lodes, and its relation to galena is seen in Xos. 348, 349, 359.
With regard to the sparry minerals of the lead veins, the specimens
show quartz (345, 349, 354, 359), calcite (349, 357), fluor-spar
(351 to 386) and pearl-spar (354). Many of the fine specimens of
fluor and galena are from the old silver-lead mines of Beer Alston,
in South Devon, which were worked on two great cross courses, or
north and south veins, and were once the centre of great mining
activity.

The specimen, Xo. 360, from Wheal Hope, near Truro, shows the
well-known pseudomorphous galena sometimes called blue lead ore
Here the lead sulphide has gradually taken the place of six-sided
prismatic crystals of pyromorphite, or lead phosphate. Such
pseudomorphs are, in some cases, hollow, the outer portion of the
crystals having been converted into galena, and the enclosed pyro-
morphite having then been removed in solution. The formation of
a sulphide after a phosphate suggests rather exceptional reactions
inasmuch as the sulphides are generally of earlier formation than
the oxidised compounds of the metal.

Galena readily suffers alteration in the shallow part of an ore-
deposit, where the sulphide is exposed to oxygen and carbonic acid,
and the most common product of alteration is the carbonate of
lead, called Cerussite. Examples of this mineral are shown in Nos.
361 to 369. Most of the specimens still retain sufficient of the
gozzany matrix to attest the superficial origin of the mineral. The

* A cubo-octahedron is a combination of the two simple forms, the cube and
the regular octahedron.

5G MINERALS OF CORNWALL AND DEVON.

cerussite occurs chiefly in long slender crystals, often acicular and
sometimes of great delicacy, and these by their snow-white colour
contrast strikingly with the dark brown limonite on which they are
displayed. Many of the finest examples are from the old Pentire
Glaze Mine, in the parish of St. Minver, in North Cornwall.

A splendid specimen of cerussite from Frank Mill's Mine, Christow,
near Exeter — presented many years ago by C. Wescombe, Esq., is
exhibited in a neighbouring pedestal-case opposite Wall-case No. 18.

The isomorphous series of phosphates, arseno-phosphates and
arsenates of lead, constituting the minerals known as Pyromorphite
and Mimetite, receive ample illustration here (Nos. 370 to 380).
Cornwall formerly yielded remarkably fine specimens of these
species, and many of the examples in this case came from the old
mine of Wheal Alfred, in the parish of Phillack, in West Cornwall—
a mine which in its day had great reputation for such specimens.
The crystals belong to the hexagonal system, and usually affect a
prismatic habit. They exhibit green, yellow and brown colours
with a lustre which, in some cases, is rather resinous, and in others
almost adamantine, as is so often the case with minerals containing
lead. The phosphate or arsenate is associated in pyromorphite and
mimetite with lead chloride.

The origin of these species is probably to be sought in the alteration
of mispickel and apatite, which has furnished, directly or indirectly,
the acid radicles to the lead of the galena. Like the phosphates and
arsenates of copper shown in the opposite division of this Case, these
lead salts are essentially the products of chemical reactions carried
on in the laboratory of the gozzan.

Silver ores (Nos. 381 to 390).

Most of the galena of Cornwall and Devon is more or less argenti-
ferous, and some of it extremely rich. According to Pryce the ore
raised at one time at Garras, near Truro, yielded lead which gave as
much as 100 ounces of silver to the ton. The rich argentiferous
galena of Beer Alston, in Devonshire, contained from 80 to 120
ounces of silver to the ton of lead, the proportion in one case rising
to 140 ounces.

It is probable that the silver in galena occurs as a sulphide, and
since the two sulphides, Ag 2 SandPbS, possess similar crystallographic
symmetry they may be associated as isomorphous growths. In
some cases, however, they seem to occur rather in the state of mere
mechanical mixture, for it has sometimes been found that the galena
becomes much less argentiferous after the ore has been well washed.*

Sulphide of silver, forming the mineral known as Argentite, has
been found, though rarely, in Cornwall. The mineral crystallises
in the cubic system, and the finest British specimens occurred at
Wheal Ludcott, an abandoned mine near Liskeard, where the cross
course yielded cubo-octahedra measuring half an inch along the edge.

* J. A. Phillips in Journ. Soc. Arts, April 27, 1859,

SILVER-ORES. 57

it is from this mine that No. 381 was obtained. No. 382 is a
specimen of Pijrargijrite, or dark red silver-ore, a sulphantimonite of
silver, of rare occurrence in Britain. This specimen came also from
Wheal Ludcott. The late Mr. Thomas Davies of the British
Museum, described the occurrence of Step/ianite at this mine— the
first recorded occurrence of crystals of this species in Britain.* This
mineral is likewise a sulphantimonite of silver, and was found
at Wheal Ludcott, associated with argentite and native silver. Far
finer specimens, however, were afterwards obtained from Wheal
Newton, near Callington — a mine which yielded the magnificent
crystal preserved under a glass shade in Wall-case No. 14. This
specimen was the subject of a memoir by Prof. W. J. Lewis. f

In the early part of the last century, silver-ore was discovered in
quantity in a cross-course at Wheal Herland, near Gwinear.J About
108 tons were extracted from a depth of between 110 and 142
fathoms. The minerals included galena, argentite and native
silver, with bismuth and cobalt ore.

Small veins, rich in argentiferous galena and occasionally carrying
true silver-ores, have been worked at Duchy Peru in Perranzabuloe.
The veins are cross-courses, running north and south, and inter-
secting the great iron-lode, most of the silver-ore being found near
the intersection.^

According to Mr. Joseph Carne, the first discovery of silver in
Cornwall was made about 1788, in a mine in the parish of Perran-
zabuloe, " which was in consequence dignified with the name of
Huel Mexico."||

Dolcoath and Wheal Duchy, near Callington, are other mines
which have yielded silver-ore in commercial quantity, the latter
mine having produced native silver, argentite and red silver ore, or
pyrargyrite.

Silver in a free or native condition has not infrequently been
found in Cornish mines, but usually in only very small amount.
Several examples of Native Silver are here shown (Nos. 383 to 386).
The sdver is mostly in a capillary form, in thin hairs or stiff wire,
often twisted, and occasionally like " moss copper." It is invariably
a secondary mineral, and may have been reduced from the state of
sulphide or deposited from silver salts in solution. Prof. Vogt, who
has carefully studied the occurrence of native silver at the famous
mines of Kongsberg in Norway,^} believes that direct crystallisation

* Geol. Mag., vol. iii. (1866), p. 432.

f " On a Crystal of Stephanite from Wheal Newton." Proc. Camh. Phil.
Soc., vol. iv. (1883), p. 240.

\ " Account of the Discovery of Silver in Herland Copper .Mine." By
the Rev. Malachy Hitchins. Phil. Trans., vol. xci. (1801), p. l."9.

§ "' The Duchy Peru Lode, Perranzabuloe." By Warington Smyth, M.A.,
F.R.S. Trans. R. Geol. Soc. Corn., vol. x. (1887), p. 120.

:; Trans. R. Geol. Soc. Corn., vol. i. (1818), p. 121.

1 " XJehir die Bildung des gediegenen Silbers, besondyrs des Kongsberger
Silbers durch Secundarprocesse aus Silb:rglanz und anderen Silbererzen."
J. prakt. Geol, April, 1899, p. 113.

58 MINERALS OF CORNWALL AND DEVON.

from solution is not common, and that the metal has usually passed
through the condition of sulphide. Much of the capillary silver in
the Cornish veins may possibly have been derived, like the similar
forms of native copper, from circulating solutions, through the
reducing action of ferrous salts or perhaps metallic sulphides.
Haloid combinations of silver are often found native, and in Corn-
wall the chloride has been recorded from a number of localities.
This compound is known commonly as horn silver, and technically
as Cerargyrite — names suggested by the soft and sectile character of
the substance, which can be cut as readily as a piece of horn. It
crystallises in the cubic system, and is usually found as an incrusta-
tion on other minerals. In most of the specimens shown here (Nos.
387 to 390) the cerargyrite is spread over an ochreous matrix, thus
testifying to its superficial formation as a mineral of the gozzan.
Although rather unattractive to the eye, the mineral is one of the
first importance among silver ores, inasmuch as it contains when
pure three -quarters of its weight of silver. In Cornwall, however,
it occurs generally in only small quantity, but at the present time
(1904) a deposit of silver ore, chiefly cerargyrite, is being worked, in
a north and south vein, at the Perran Mines, Marazion. No. 387 is
a sample of this ore, presented by 6. D. McGrigor, Esq.

Zinc-ores : Blende and Calamine (Nos. 391 to 403).

As " blende " is a name of rather general significance applied to
several minerals, the sulphide of zinc, which is the commonest of all
blendes, is termed for distinction's sake zinc blende. The name
Sphalerite, given to it half a century ago by Haidinger, has been
revived in recent years, and is now frequently used in place of
" blende." By miners in Cornwall, as elsewhere, it is often known as
Black Jack.

As the number of Cornish specimens of blende shown here is not
large, and as the mineral will come prominently forward in con-
nection with the products of the North of England, but little need be
said in this place with reference to its characters. It crystallises in
the cubic system, has usually a dark brown colour, and presents a
brilliant lustre. All these characters are illustrated by Nos. 391 to
399. In No. 392 the black blende is crystallised around slender
prismatic crystals of white quartz. Chalybite is associated with the
zinc ore in No. 400. The iron-bearing variety of blende from St.
Agnes, called Marmatite, is seen in No. 402. Instead of being
crystallised, the blende of Nos. 397 and 401 is in mammillary forms ;
whilst No. 401 is also exceptional in presenting a white colour.

By exposure to meteoric agencies the sulphide of zinc may become
altered to carbonate — thus forming a substance sometimes known
to mineralogists as Calamine. No. 403 is an example of Cornish
calamine. It is not, however, a common mineral in Cornwall and
Devon ; but the visitor will find it prominent among the ores of the
Mendip Hills and of Derbyshire, and further description may,
therefore, be deferred until these ores fall undernotice (pp. 109, 141).

ANTIMONY-ORES. 59

Antimony ores (Nos. 404 to 408).

Antimony— a metal which forms with arsenic and bismuth an
alliance of brittle metals — occurs in nature usually as a sulphide,
forming a mineral known variously as Stibnite, antimonite, grey
antimony ore or antimony glance. In some of the cross veins which
course in a north and south direction through the killas of north-
eastern Cornwall, especially near Padstow and Tintagel, this mineral
was at one time not by any means infrequent. The specimen No.

404 is from Endelhon. The Cornish stibnite is either massive,
fibrous, or in inconspicuous crystals. From such specimens it is
refreshing to turn to the noble crystals of this species, which startled
mineralogists when they were first brought some years ago from
Japan. Of these Japanese crystals a fine example is exhibited in a
neighbouring Case, sufficiently illustrating their remarkable size,
form and lustre.

In the antimony-bearing veins of Cornwall the metal occurs not
only combined with sulphur as stibnite, but associated also with
sulphide of lead. The mineral so formed was named by Haidinger,
J amesonite, after Robert Jameson who was for so many years pro-
fessor of mineralogy in Edinburgh (b. 1774, d. 1854). The specimens

405 to 407 show this species as a fibrous substance of steel-grey or
iron-black colour and metallic lustre, not altogether unlike fibrous
stibnite. It may be regarded as a sulph-antimonite of lead, or as a
double sulphide containing, according to Rammelsberg, 2PbS. Sb^S ,
having therefore the formula of galena and stibnite. *

The yellow amorphous mineral in No. 408 is a hydrous lead anti-
monite, known as Bindheimite or Bleinierite. It is evidently an
oxidation product resulting from the alteration of Jamesonite, with
which it is often associated, as seen in Nos. 406 and 407, where the
metallic mineral is partially encrusted with the yellow antimonate.

* See. however, a paper by Mr. L. J. Spencer and Mr. G. T. Prior, in
)lin. Mag., vol. xii. (1900), p. 58.

60 MINERALS OF CORNWALL AND DEVON.

CASE IV.

DIVISION I,
MINERALS OF CORNWALL AND DEVON.

Sulphides and Sulpho-Salts.

(Nos. 409 to 475).

Several metallic sulphides — including those of tin, copper, lead,
zinc and antimony — have been already noticed in the descriptions
of Cases I. to III., in which they are exhibited. A few other sulphides,
such as iron pyrites, with certain sulpho-salts, are grouped together
in the Case now under description. Iron-pyrites, the most widely
diffused of all metallic sulphides, is not peculiar to any particular
type of ore deposit, and has therefore been left without special
notice in the preceding pages. The sulpho-salts here exhibited
include bournonite, tetrahedrite, and tennantite — and as these
species are found usually in lead -veins, and contain antimony and
arsenic, they stand in close relationship to the minerals exhibited
in the Case immediately preceding (No. III.).

Pyrite (Nos. 409 to 428).

Pyrite is the name now frequently employed by mineralogists to
designate the mineral which is commonly known as iron-pyrites.
This species consists of iron disulphide, crystallising in the cubic
system, and some very bold examples of the crystals are shown in
this Case. In the mineral-veins of the West of England, pyrite is
one of the commonest constituents, and is termed by the miners
mundic. According to Borlase " the Cornish name is Mundic,
from the cleanly shining appearance both of its surface and struc-
ture."*

Pyrite is a mineral widely distributed through most rocks, whether
eruptive or sedimentary, in some cases as an original mineral, in
others as a secondary product. As a vein-mineral its formation
appears to have extended from the earliest to the latest stages in the
history of the lode. In some cases the pyrite may be of primary
origin ; in others it has been introduced at a later date, evidently
deposited from solution on other minerals, encrusting or replacing
them, as witnessed by such pseudomorphs as Nos. 426 and 427 ;
and in yet other cases the pyrite may be of comparatively recent

* " The Natural History of Cornwall." Oxford : 1758, p. 131.

PYRITE. ''"I

origin, due to the reduction of solution of a sulphate, though
probably this mode of origin is not so common in veinstones as in
sedimentary rocks. Stalactitic pyrite has occurred at East Pool.

Xos. 414 and 415 show the pyrite crystallised on quartz, whilst in
Xo. 41'J the quartz has crystallised on the pyrite. In No. 425 pyrite
has been deposited on large cubes of fluorspar, forming a brass-like
coating with a drusy surface. Xo. 426 is a hollow epimorjih of pyrite
after calcite, and Xo. 427 one of pyrite after baryte ; the mineral
originally invested having in both cases been completely removed,
leaving a pyritous shell. *

Pyrite commonly crystallises in cubes, as shown in Xos. 410, 415 and
416. In Xo. 410 the cubes measure more than an inch along the edge.
The fine specimen Xo. 409 shows the regular octahedron in combina-
tion with the cube. Xo. 413 is an excellent example of sharply
defined crystals in form of the pentagonal dodecahedron, which is a
hemihedral form of the four-faced cube, so characteristic of pyrite
that it was called by Haidinger the pyritohedron. A hemihedral
form of the six-faced octahedron is known as the dyakis-dodeca-
hedron, or diplohedron ; this is also characteristic of pyrite, but
though occasionally occurring as an independent form it is usually
found in combination. The " Pyrites group " consists of a few
closely allied minerals, assuming these hemihedral forms : and since
each face of the pentagonal and the dyakis-dodecahedron has an
opposite parallel face the group is said to present " parallel faced
hemihedrism."f

Most of the specimens exhibited in this Case show the
brass-yellow colour of the pyrite, but in No. 419 the colour is
steely grey. The metallic lustre is illustrated by most of the speci-
mens, and in Xo. 414, where the pyrite is crystallised on quartz, the
lustre is exceptionally brilliant. Occasionally the surface becomes
coated with a brown tarnish due to superficial alteration into
limonite. Such alteration may penetrate to a considerable depth, and
ultimately the entire crystal may be converted into the brown iron
oxide. This change — one of the most common chemical changes
which pyrite suffers — is well illustrated by the specimen Xo. 428, in
which an aggregate of cubes has been transformed more or less com-
pletely into ferric hydrate with retention of the pyrite shape. The
limonitisation of pyrite contributes largely to the formation of
gozzan.

Still more unstable than pyrite is the ortho-rhombic species of iron
disulphide, known as Marcasite (No. 428). This mineral occurs
occasionally in the Cornish veinstones, but is not usually abundant,
and further reference to it is therefore deferred until the marcasite of
the sedimentary rocks has to be described (p. 108).

* An epimorph is a pseudomorph formed by the deposition of one mineral
upon another ; and is therefore simply a mechanical encrustation. Epimorphs
are known also as perimorphs.

f See Prof Miers's " Mineralogy " (p. 49) for technical definition of the
cla^s of crystals known as the " Pyrite class," characterised by " tesseral
centro - symmetry. ' '

62 MINERALS OF CORNWALL AND DEVO"J.

A fine series of specimens of pyrite will be found in Case II. of the
Ludlam Collection in the Hall of the Museum, and others in the Wall-
case No. 46 on the Principal Floor.

Mispickel (Nos. 429-436).

Although Mispickd has already been noticed as an associate of
tinstone (p. 31), it demands further reference in this place, as being
an important member of the group of metallic sulphides known
sometimes as the Pyritoids. In a pure state it is an arseno-sulphide
of iron, conforming to the simple formula Fe As S, and therefore con-
taining theoretically about 46 per cent, of arsenic. Hence it is
known as arseno-pyrite or arsenical pyrite. Struck with the pick it
emits the characteristic garlic-like odour of arsenic, and is recognised
by miners as arsenical mundic or arsenical iron, or merely as "arsenic."
Mispickel belongs to the orthorhombic system, like marcasite, with
which it seems to be isomorphous. Many specimens, as Nos. 429,
430, show the rhombic prisms sharply defined, and some illustrate
the characteristic twinning, similar to that of marcasite. The
curvature of some of the faces is very marked in No. 429. The
silver white and steel-grey colours of mispickel are fairly illustrated
by Nos. 430, 434 ; but after exposure, though less prone to alteration
than marcasite, the colour is apt to suffer. The bold crystals in No.
433 show a brilliant reddish tarnish : this specimen is from Wheal
Kitty, St. Agnes, and the mineral is here associated with copper
pyrites, coated with green carbonate, whilst chalybite, in globular
aggregates of lenticular crystals, has been deposited on certain faces
of the mispickel.

Many of the specimens show the mispickel in association with
quartz, in some cases well crystallised. The quartzose veinstone
of certain specimens, as seen here, is of cavernous structure, with
pseudomorphic hollows ; in other cases it is " peachy," that is to
say, it is associated with chlorite. Copper-pyrites may be detected
on several specimens.

By the alteration of mispickel, through the action of oxidising
agencies in the shallow parts of a lode, iron arsenates, like scorodite,
may be formed (p. 73). When the arsenide is associated with copper
ores, as is so often the case, as just mentioned, the resulting products
of oxidation may be copper arsenates, or copper-iron arsenates, such
as are illustrated by the fine display in Case III.

The importance of mispickel as an "arsenic ore," or source of white
arsenic, in the copper and tin mines of the West of England, has
already been referred to, and statistics of production given, at p. 32.

Boumonite (Nos. 437 to 456).

More than a century ago, the beautiful mineral now called Bour-
nonite was figured by Mr. Rashleigh in his work on the Menabilly Col-
lection * — a collection recently added to the Museum of the

™ * Rashleigh's " Specimens of British Minerals," 179' PI. xix. figs. 1 and
2, p. 34.

BOl KNOXITE. W>

Royal Institution of Cornwall at Truro. His specimens were
obtained from Wheal Boys, in the parish of Endellion, in the killas
country of North-east Cornwall. It was from this locality that the
specimens here shown as Xos. 437 and 438 were derived. The
mineral occurred there in association with zinc blende, jamesonite,
chalybite, etc.

Described by Rashleigh as "an ore of antimony" it was recognised
as a distinct species by the Comte de Boumon, a French refugee
living in this country in the early part of the eighteenth
century.* By de Bournon it was called from its locality endellione,
whence the name Endettionite, sometimes applied to this species.
This name, however, has generally given place to Jameson's name
bournonite, in recognition of the mineralogist who first described it
with accuracy.

The original specimens from Endellion were eclipsed by the much
finer examples raised many years ago at Herodsfoot Mine, about
seven miles S.W. of Caradon in East Cornwall. In this silver-lead
mine, the lode ran through killas, with a bearing about 20° E. of north,
and the argentiferous galena for which the mine was worked occurred
in a quartz veinstone, where it was associated with pyrite, blende,
occasional bunches of rich copper ore, and certain antimonial
minerals. The antimony ore occurred just below the gozzan, and
being detrimental to the lead was regarded as a nuisance. f

An analysis of the Herodsfoot bournonite by Mr. C. E. WaitJ
showed that it conformed to the recognised formula CuiPb z Sb 2 S„ '
the antimony being replaced to a small extent by arsenic. It may
be regarded as a sulphantimonite of lead and copper.

Bournonite crystallises in the orthorhombic system ; and some
noble crystals, remarkable not only for size but for complexity of
form and brilliancy of certain faces, are exhibited in this Case. The
crystallography of the Cornish bournonite has been exhaustively
studied by Professor Miers.il Twin groups are very common, giving
rise in some cases to cruciform, stellate and circular discs, which are
known as cog-wheel-ore, as illustrated by Xos. 441, 442, 445
and 446.

A hint as to the possible genesis of bournonite may be obtained
from certain pseudomorphs having the form of tetrahedrite but the
composition of bournonite, thus suggesting that under certain cir-
cumstances bournonite may have been derived from the alteration
of tetrahedrite.

a ~* " Description of a triple sulphuret of Lead, Antimony and Copper from
Cornwall." By the Count de Bournon, F.R.S. Phil. Trans., vol. xciv.
(1804), p. 30. Also Analyses by Hatchett, Ibid., p. 63.

-)■ " On the Metalliferous Associations of the Liskeard Bocks.'' By Mr.
John Giles. Trans. Roy. Geol. Soc. Corn., vol. vii. (1865), p. 198.

% " Analysis of Bournonite." Chem. News, vol. xxviii. (1873), p. 271.

i This is equivalent to 2 PbS. CujjS.SbjS,.

,i " The Crystallography of Bournonite!" By H. A. Miers, M.A., Min.
Mag., vol. vi. (1884), p. 59.

64 MINErtALS OF CORNWALL AND DEVON.

Tebrahedrite and Tennantite (Nos. 457 to 475).

Tetrahedrite is known sometimes as grey copper ore, but this term
is ambiguous since it is also occasionally applied to copper glance.
The name tetrahedrite refers to the regular tetrahedral form which
the crystals usually present. Grand examples were obtained at one
time from Herodsfoot Mine, where the mineral occurred in associa-
tion with the bournonite just described. A fine suite of the Lis-
keard tetrahedrites is here exhibited (Nos. 457 to 468). The regular
tetrahedron is usually bevelled on the edges by planes of the three-
faced tetrahedron. It will be noted that the crystals are coated in
most cases with minute crystals of chalcopyrite, producing a
rough drusy surface ; and that the chalcopyrite frequently displays
a brilliant iridescence, due to superficial conversion into " peacock
copper." When the mineral was first raised the colours were often
gorgeous, but the effect became impaired by exposure. The
encrusting copper pyrites seems to have been derived from the
alteration of the tetrahedrite.

The chemical composition of tetrahedrite is very complicated,
and the crystals are often wanting in homogeneity ; but it may be
regarded as essentially a sulphantimonite of copper, in which the
copper is partially replaced by iron, zinc or even silver, whilst the
antimony is more or less replaced by arsenic. Recent analyses by
Mr. G. T. Prior* have led to a new formula, which admits of simplest
expression in the form Cu, Sb S 3 .

Tetrahedrite is likewise known under the name of fdhl ore — a name
borrowed from the German Fahlerz, which is now regarded as a
general term applied not only to the copper sulphantimonite but also
to the corresponding sulpharsenite. When arsenic is substituted for
antimony, the mineral is called Tennantite. The old name fahl-ore
consequently includes both tetrahedrite and tennantite, with
isomorphous mixtures of the two. In some tennantite bismuth is
present. Tennantite received its name from a famous English
chemist, Smithson Tennant (h. 1761, d. 1815). The specimens Nos.
469 to 475, from Wheal Jewel in Gwennap, illustrate the characters of
this mineral, and show its association with quartz and copper pyrites.

Excellent crystals of tetrahedrite, having all the characteristics of
the Cornish mineral, were found on the ancient Roman bronze coins
which Daubree described, from the thermal springs of Bourbonne-
les-Bains (Haute Marne). The alteration of the bronze yielded not
only tetrahedrite, but also chalcosite, chalcopyrite and erubescite.

No.476 is a specimen of Condurrite, a mineral described by Faraday,
from the Condurrow Mine, Camborne. It is a black amorphous
mineral, so soft as to soil the fingers. Chemically it is chiefly a
copper arsenide, but seems to be a mixture rather than a definite
species, and has been regarded as an alteration-product derived
perhaps from tennantite.

* " The Identity of Binnite with Tennantite ; and the Chemical Composi-
tion of Fahlerz." By G. T. Prior, M.A., and L. J. Spencer, M.A. Min. Mag.,
vol. xii. (1900), p. 184 (Fahlerz, p. 193).

ORES OF IRON. (55

DIVISION 2.

MINERALS OF CORNWALL AND DEVON.

Ores of Iron, etc.

(Nos. 177 to 544.)

Ores of iron enjoy a wider distribution than the ores of anv
other metal. They occur both in eruptive and in sedimentary rocks
and are not restricted in the latter to any special horizon. Never-
theless, in Cornwall and Devon, the accumulation of suitable
minerals in the form of workable ore-bodies is rather limited ; and
at the present time no iron ore is being raised in Cornwall, and only
an insignificant quantity in Devonshire.

Most of the fine specimens exhibited in this Case were obtained
many years ago from the famous mine near Lostwithiel, which was
known, after Queen Victoria's visit in 1840. as the Restormel Royal
Iron Mine. The great iron lode, generally in two branches, is a
cross course in killas, bearing about 15° W. of N, and having a dip
to the east of between 70"' to Ho'.* The branches formed practically
two parallel veins, the principal lode being in some parts more than
2u feet wide. The ore was carried in a quartzose veinstone, which
abounded in vu<rs or drusy chambers, often lined with beautiful
crystals. t It was from the walls of such cavities that the specimens
here exhibited were taken. The ore was chiefly hematite, with
g ithite and limonite, accompanied occasionally by black oxide of
manganese and Iithomarge, in small pockets.

Extensive workings for iron-ore were also made in Cornwall on
the Great Perran Lode, or the Duchy Peru lode, in Perranzabuloe.
This vein extends for several miles in a direction which is approxi-
mately W.N.W. andE.S.E., and has in some partsawidth of as much
as 120 feet. The lode courses through killas, and consists principally
of a brecciated quartzose veinstone holding much chalybite, or
carbonate of iron, which passes into brown iron-ore in the upper part
and is associated with large quantities of zinc blende and a little
copper-ore. j Both in this lode, and in the Restormel iron-lode,
pseudomorphous quartz is abundant, testifying to the chemical
changes which must have been rife since the original formation of the
veins.

Magnetite (No. 477).

Two anhydrous oxides of iron occur native — one called magnetite
(Fe s <),), comparatively rare in this country; the other termed
haematite (Fe 2 3 ), fairly abundant, and in the North of England
largely worked as an ore.

* Henwood, Trans. R. Geol. Hoc. Corn., vol. v. (1843), p. 128.

t A drusy surface is one coated with small crystals. A cavity lined with
crystals is known as a druse ; or if rounded it is often termed a geode.

* See Sir W. W. Smyth's papers, " On the Iron Mines of Perran." Trans.
R. Geol. Soc. Corn., vol. vii. (1865), p. 332 ; and " The Duchy Peru Lode, Per-
ranzabuloe." Ibid. vol. x. (1887), p 120.

7S82. F

66 MINERALS OP CORNWALL AND DEVON.

Magnetite occurs as a constituent of nearly all eruptive rocks
and is especially notable in the dark-coloured dense rocks of basic
type. It must have separated from the molten magma in most cases,
at an early phase in the consolidation, for it occurs as enclosures in
nearly all the other .rock constituents. This priority of crystallisa-
tion, however, was not invariable ; and Dr. Teall has shown, for
example, that in some of the basaltic rocks of Franz Josef Land the
magnetite was the last mineral to crystallise.*

Whilst magnetite is thus abundant in microscopic crystals and
grains, it is by no means common, in this country, in macroscopic
crystals. No. 177 shows, rather exceptionally, some bright little
octahedra of Cornish magnetite. Strings of magnetic iron-ore
occasionally seam the rocks of the south-western counties, and
declare their presence by disturbing the compass of a passing tourist.
In South Devon such ore is sometimes found in quantity sufficient to
invite exploration. Sir C. Le Neve Foster has described the iron-ore
of Haytor, on the eastern border of Dartmoor, as occurring in the
form of thick beds of magnetite, interstratified with altered shales
and sandstones of Carboniferous age.f The formation of the magne-
tite by metamorphism of other ores may be connected with the
intrusion of a mass of granite. The surrounding rocks are much
silicified and contain hornblende, garnet, axinite and some other
minerals. -There are three beds of ore, with an aggregate thickness
of 26 feet.

In describing the bedded deposits of iron ore at Smallacombe, in
Devonshire, Mr. J. H. Collins has expressed his opinion that the ore
was originally a carbonate of iron which has become altered to
magnetite by the action of circulating waters. J It is well known
that iron ore carrying the metal as carbonate, such as spathic ore or
even clay ironstone, becomes magnetic on calcination ; and it is not
unlikely that magnetite may in some cases be formed from chalybite
by contact with basalt or other rocks at even moderate temperature.

Magnetite may likewise result from the deoxidation of haematite
by means of ferrous compounds or other reducing media. Pure
haematite contains 30 and magnetite 28 per cent, of oxygen ; so that
the transformation does not necessitate a great amount of deoxida-
tion. On the other hand, pseudomorphs of haematite after magne-
tite show that the converse change may take place. Martite, which
is a red oxide of iron in crystals like those of magnetite, has
probably such an origin. If not a pseudomorph, Fe.,0,; must be
dimorphous.

On the disintegration of the crystalline rocks, the magnetite
which they contain tends, by its density and comparative stability,
to accumulate locally in the detritus. Hence the origin of the black

* " Notes on a Collection of Rooks and Fossils from Franz Josef Land."
Quart. Journ. Geol. Soc, vol. liii. (1897), p. 477.

f " Notes on Haytor Iron-mine." Quart. Journ. Oeol. Soc, vol. xxxi. (1875),
p. 628.

% Rep. Min. Assoc. Corn., 1872.

HKMATITE. '17

magnetic sand found on the Cornish coast, as near Botallack. Such
sands may contain also titanic iron on- or Iserine. A similar mineral
called Menaeeanite takes its name from Menaccan, near Helston in
Cornwall, where it was found as sand in a stream at Tregomvell
Mill.

Haematite (Xos. 478 to 4*1).

Under the name of H'xmatite slth included all the varieties of native
ferric oxide, which are either crystallised in the hexagonal system or
are merely massive. The crystals have often the brilliancy of
burnished steel, whence the name specular iron, iron glance or looking
glass ore This splendent lustre may be seen on the small crystals
here exhibited (Xos. 478 to 480). Most of these are from Botallack
Mine, and show the specular mineral implanted, as in many other
localities, on quartz. In No. 470 the mineral is associated with fine
bisphenoids of chalcopyrite on hexagonal prisms of quartz. The
mines of Cumberland yield crystallised specimens of this mineral so
much finer than anything found in the Cornish mines that fuller
description of the substance may be fairly deferred until the North
of England minerals are noticed (p. 144).

A variety of specular haematite occurring in very fine scales is
known as micaceous iron ore. Such a mineral occurs in Devonshire,
near Bovey Tracey, and it is recorded that large quantities were sent
to London, " in the days of pounce,"* and sold as Devonshire sand.
In recent times considerable quantities have been raised in Devon-
shire under the name of '' shining ore,'' and exported to Germany.
The specimen No. 481 shows the character of the substance. It
is rather like finely divided plumbago, and may be used as a lubricat-
ing agent, but it is probably employed mostly as a pigment for iron-
work. It occurs in narrow lodes in granite. f

Of massive haematite or red iron ore, specimens from Restor-
mel may be seen in Nos. 493 to 41)5, which show the mineral
associated with the hydrated oxides — gothite and limonite. In
some cases haematite may have been derived from such hydrates by
natural removal of water ; but the converse change, the hydration
of red ore, is also frequent. Mr. Solly has described pseudomorphs
of haematite after pyrite from Torquay.^ The conversion of the
sulphide into limonite is common enough, but its alteration to
haematite is exceptional, and it is suggested that the haematite
was there formed by the reaction of limestone on ferric chloride, due
to the alteration of the pyrites by sea water.

* "The Economic Geology of Devon," By R. X. Worth. Trans. Devon
Assoc, vol. vii. (1875), p. 225. De la Beche's Report on Cornwall, p. 617.

-f " Micaceous Iron-ore, near Bovey Tracey." By Mr. Joseph S. Martin.
Trans. Manch. Oeol. Soc, vol. xxiii (1895), p. 162.

+ "Pseudomorphs of H-ernxtite after Iron Pyrites." By R. H. Solly, M.A..
with an analysis by A. Hutchinson, B.A. Min. Ma;/., vol. viii. (1889),
p. 183.

7882. F 2

68 MINERALS OF CORNWALL AND DEVON.

Guthite and Limonite (Nos. 482 to 500).

The specimens Nos. 482 to 492 present a fine series of specimens
of Gothite, a rather rare mineral, of which Cornwall has furnished
typical examples, of exceptional beauty. This mineral is composed
of peroxide of iron with about 10 per cenl of water, or it may be,
regarded as ferric hydrate or hydrate of iron. It crystallises in the
orthorhombic system, and good crystals are shown from Botallack
and St. Just as well as from Restormel. Its occurrence in aciculai
crystals, forming fibrous aggregates, has led to the name needle iron
ore : the uniform mass No. 992 exhibits this fibrous structure. In
No. 491 the surface presents a velvety appearance, rather like that
of the Bohemian variety, which is known from this character as
Sammetblende. The name gothite, given to this mineral a century
ago in honour of the poet, recalls the interest which he took in
mineralogy, as in other branches of natural history.

The association of gothite with other minerals in a regular succes-
sion of deposits is beautifully illustrated by the specimens Nos.
493 to 496 from the Restormel Royal Iron Mine. The sequence
shows (1) crystallised quartz, (2) fibrous' limonite or wood iron
ore, (3) crystalline gothite, (4) compact haematite. These
minerals have evidently been deposited in regular succession on the
walls of a vug or cavity in the veinstone, and the successive zones
are sharply separated from each other by differences of colour —
white, brown, black and red — almost as marked as in the banded
deposits of an agate.

Limonite, or brown iron ore, is a hydrated oxide of variable com-
position, conforming in the purest varieties to the formula 2 Fe 2 5
.'3H 2 0, thus differing from gothite, Fe 2 3 . H 2 0, by containing nearly
5 per cent. more water. Unlike gothite,it never occurs in distinct crys-
tals, but fibrous forms are not uncommon. Some beautiful examples
of this wood iron ore, or fibrous limonite with radial and zonal
structure, hair-brown in colour and silky in lustre, are shown in the
Restormel specimens Nos. 498 and 499. Limonite frequently occurs
in stalactitic forms, clearly pointing to its deposition from water ;
and a specimen of this character, numbered No. 497, is interesting
in that the surface of the stalactites is sprinkled over with small
crystals of native copper. No. 500 is an example of the ochreous
limonite, of yellowish-brown colour and loose texture, known as
bog iron-ore — evidently a superficial deposit of recent origin. The
brown iron ores will receive further notice in the description of the
minerals of the sedimentary rocks (see p. 193).

In mineral-veins where pyrites and chalybite are common, as in
Cornwall and Devon, the formation of limonite, and of other oxides
and hydroxides of iron, presents no difficulty, inasmuch as they are
evidently minerals of secondary origin, and so unstable a body a«
pyrites may well have been, in many cases, their original source •
whilst in other cases the oxides may have resulted from the alteration
of carbonate of iron.

CHALYBITE. 69

Chalybite (Xos. 501 to 51 G).

Iron occurs in the lodes of the West of England not infrequently
in the form of carbonate, constituting the mineral known as Chalybite
or Hiderite. This mineral crystallises in the rhombohedral system ;
carbonate of iron taking its place with the carbonates of calcium,
magnesium, zinc, and manganese, in the isomorphous group of
rhombohedral carbonates.

Cornwall is rather famous for its crystallised chalybites, and an
excellent and extensive collection is here exhibited. The crystals
are usually of rhombohedral habit, and not of very complex form.
Acute rhombohedra occur in some specimens, and the basal plane
is a feature in others. Certain crystals simulate the appearance of
regular octahedra. No. 513 is a characteristic example of lenticular
chalybite, the obtuse rhombohedra having curved faces ; whilst No.
514 shows the mineral in a fibrous form.

Dr. A. Hutchinson has recently examined the chemical composi-
tion and optical characters of a series of well crystallised specimens
of chalybite from near Camborne, now in the mineralogical
museum of the University of Cambridge.* According to Prof.
Xoel Hartley and Mr. Eamage, the chalybite of East Pool Mine
contains such rare metals as indium and rubidium, with cobalt,
nickel, bismuth,, etc. j 1

Well known to collcr-tors, but now extremely rare, are the zoned
crystals of chalybite. found at one time at Wheal Maudlin, near
Lostwithiel, represented by No. 512, and also by several fine speci-
mens in the Ludlam collection in the Hall, Case VI. They are
hexagonal crystals of tabular habit, seated on quartz from the walls
of a geode, and are remarkable for the fact that the basal plane,
which is slightly curved, displays a series of zones of various shades
of brown, forming concentric hexagons.

The association of chalybite with copper pyrites is seen in No. 503,
with fluorspar in Nos. 507 and 508, and with quartz in many speci-
mens such as Nos. 501, 506, 509, and 511. In No. 510 the chalybite
is crystallised on a group of prismatic crystals of quartz.

Much history may be read in such a specimen as No. 515, from
Virtuous Lady Mine (afterwards the Bedford United Mines), near
Buckland Monachorum, in South-western Devonshire. This is one
of the well-known " boxes." It is evident that this was originally
a large cubic crystal of either fluorspar or iron pyrites, probably the
former, since this mineral not infrequently assumes such bold cubic
forms. I Upon this cube there was deposited, from solution, a rather
thick coating of crystalline chalybite. Then the fluorspar was
dissolved out, leaving a hollow shell of carbonate of iron. Into this

* " The Chemical Composition and Optical Characters of Chalybite from
Cornwall." By A. Hutchinson, M.A., Ph.D. Min. Mag., vol. xiii. (1303;,
p. 209.

f Journ. Chem. Soc., vol. lxxi. (1897), p. 533.

t Traces of fluor have been found in some of the hollow cubes.

70 MINERALS OF CORNWALL AND DEVON.

cubic " box," silica was introduced, and formed a group of prismatic
crystals of quartz on one of the inner walls. Finally, there was
deposited upon this quartz some bold bisphenoids of copper pyrites,
now superficially tarnished.

It must be admitted that as ferrous carbonate is rather soluble in
most waters it is not easy to understand the nature of the solvent
which could remove fluorspar whilst leaving the chalybite un-
attached.

In addition to the boxes, Virtuous Lady Mine yielded a number of
other hollow epimorphs, which from their shape were called
" slippers." No. 516 is an example. Here the nature of the original
mineral is uncertain ; but though selenite has been suggested, it was
more probably tabular barytes. The mineral, whatever its nature,
became encrusted with chalybite, and was then removed, leaving a
pseudomorphous hollow. The surface of the chalybite in this
specimen is brightened by a partial sprinkling of iron pyrites.

Several other examples of these interesting epimorphs, including
some much larger than those shown here, will be found in the Wall-
case No. 33, on the opposite side of the Principal Floor.

Experiment shows that carbonate of iron may be precipitated in
rhombohedral crystals, not unlike those of chalybite, by the re-
action of an alkaline carbonate on ferrous sulphate. Such a sul-
phate, resulting from the oxidation of pyrites, is common in mine
waters, whilst carbonates are carried in all surface drainage, and
in underground waters circulating throughout the zone of oxidation.
In some cases, however, the chalybite occurs at considerable depths
in mineral-veins.

Ferrous carbonate is not characterised by great stability, and
tends to pass, under the influence of air and water, into the condition
of ferric hydrate : hence the deep brown colour on the external part
of many chalybite crystals. If manganese be present, as it often is,
the coating may become nearly black.

Vivianite (Nos. 517 to 524).

Vivianite is a mineral which was originally named by Werner after
J. G. Vivian, who discovered it in Cornwall. Some very fine crystal-
lised specimens are here exhibited. The crystals belong to the
monoclinic system, and offer perfect cleavage parallel to the clino-
pinacoid. Most of the specimens show a fine indigo-blue colour ;
but it is probable that pure vivianite, which is a hydrous ferrous
phosphate, is colourless, and that the blue tints are developed by
some of the iron passing, on exposure, into the ferric condition.
Analyses of Cornish vivianites have been published by Prof.
Maskelyne.*

Most of the specimens shown here were obtained from Wheal
Jane, near Truro, and show the vivianite associated with quartz,
pyrite, mispickel, and chalybite. Two cleavable masses, exhibiting

* " Mineralogical Notices," By Prof. N. Story-Maskelyne and Dr. Walter
Plight. Journ. Chem. Soc, [2] vol. ix. (1871), p. 6.

LUDLAMITE, ETC. 71

the foliated structure of the mineral, are in the tray No. 524. In Xo.
520 a thin flat blade of blue vivianite appears to impale a crystal of
quartz ; the quartz having been deposited around a pre-existing
crystal of the phosphate.

The soft pulverulent nodular mass of vivianite in the tray Xo. 524
represents the blue iron earth, not infrequently found in peat mosses,
with bog iron ore. This earthy vivianite is often very pale, nearly
white, when first dug up, and acquires its Berlin blue colour by
exposure. When found with fossil bones, by no means an uncommon
association, its origin is obvious.

Ludlamite, etc. (Nos. ~yl~> to 520).

In 1876 the late Mr. Frederick Field gave the name of Ludlamite
to a new Cornish mineral, in compliment to Mr. Henry Ludlam,
whose extensive collection of minerals passed into the possession of
the Museum of Practical Geology, by bequest, in lttwO. A fine series
of specimens is here exhibited.

Ludlamite is a green transparent mineral, crystallising in the
monoelinic system, and consisting, according to Mr. Field's analysis,
of a hydrous ferrous phosphate. The crystallography of the
mineral was studied by Prof. Maskelyne.f

The specimens of ludlamite here shown were obtained by .Mr.
Tailing from Wheal Jane, in the parish of St. Kea, near Truro. The
associated minerals, as seen in most of these specimens, include
quartz, chalybite, vivianite, pyrite and mispickel. The conditions
of occurrence are indeed identical with those of the vivianite, ex-
hibited alongside these specimens. The two iron phosphates have,
however, certain characters by which they are readily separated,
such as the colour and the habit of the crystals.

Moreover, on exposure to heat, ludlamite decripitates and breaks
up into brilliant crystalline plates of an intense bluish green colour,
whereas vivianite similarly treated turns white and exfoliates.

The mineral called Dufrenite, in honour of the French mineralo-
gist Dufrenoy, is represented by Xo. 529 — a specimen from Wheal
Phienix, near Liskeard. This is a hydrous phosphate of iron,
which has been analysed by Prof. Kinch.*

ChUdrenite (Nos. 530 to 532).

The rare mineral ChUdrenite was first described by Levy, from
specimens discovered at the beginning of the nineteenth century in
cutting a canal near Tavistock in Devonshire. Soon afterwards it
was found at Crinnis Mine, near St. Austell, where it occurred in

* "On Ludlamite, a new Cornish Mineral." By F. Field, F.R.S. Phil.
Mag., [5] vol. iu. (Jan. 1877), p. 52. Also Proa. Cryst. Soc, part i (1877).
p. 23.

f " Note on the Optical Characters of Ludlamite." By N. S. Maskelyne,
M.A., F.R.S. Phil. Mag., Feb. (1887), p. 135.

% " On a New Variety of Mineral from Cornwall." By Prof. E. Kincb and
F H.Butler, M.A. Min. Mag., vol. vii. (1887), p. 65. " On Dufrenite from
Cornwall" By Prof. E. Kinch. Ibid., vol. viii. (1889), p. 112.

72 MINERALS OF CORNWALL AND DEVON.

association, with apatite — an association not without suggestive-
ness, seeing that childienite is also a phosphate. Many years passed
without any fresh discovery, and it remained a mineral of great rarity
until the late Mr. Tailing re-discovered it near Tavistock, and
afterwards in larger crystals at the George and Charlotte Mine,
between Tavistock and Callington. It has also been found at Wheal
Crebor and at the Devon and Cornwall United Mines.

All the specimens here exhibited are from the neighbourhood of
Tavistock, and show the mineral accompanied by chalybite, pyrite,
quartz and chlorite. Childrenite is a hydrated phosphate of iron
and aluminium, often with manganese.* It occurs in brilliant
little crystals of pyramidal habit, belonging to the orthorhombic
system, and presenting a yellow or brown colour which gives it
rather "the" appearance of chalybite, from which it differs, not "only
in crystalline form, but in greater hardness. A closely allied mineral
found at Branchville, Fairfield Co., Conn., U.S.A., has been de-
scribed by Profs. Brush and Dana under the name of Eosphorite.f
It contains, however, much more manganese and less iron than
childrenite.

The name childrenite, given originally by Levy, was compli-
mentary to Mr. John George Children, who was for many years an
officer of the British Museum, first in the department of antiquities
and afterwards in that of zoology, and who was at one time Secretary
of the Royal Society (b. 1777, d. 1852).

Pharmacosiderite (Nos. 533 to 536).

In William Phillips' paper on Cornish cuprite, published by the
Geological Society in 181 l,t the author describes and figures the
" arseniated iron," which came afterwards to be called Pharmaco-
siderite, a name proposed by Hausmann in consequence of the
poisonous character of the arsenic ((papftanov, pharmakon, poison).
The mineral is easily recognised by its occurrence in small sharply
defined cubic crystals, of green colour, whence the name cube ore,
often applied to this species. The Cornish pharmacosiderite had
previously been noticed by the Comte de Bournon,§ and an imperfect
analysis, probably of an impure specimen, was published by
Chenevix.H

The mineral may be regarded as a hydrated ferric arsenate, and the
specimens here exhibited show, by their occurrence on gozzan, that
it is an alteration product formed in the upper part of the veins, and
therefore may be of comparatively recent origin. A very careful

* An analysis by Prof. Church will be found in J own. Ohem. Soc, [2] vol. xi.
(1873), p. 103.

f im! J own. Soc, xvi. (1878), p. 35.

% Trans. Oeol. Soc, vol. i. (1811), p. 23.

§ " Description of the Arseniates of Copper and of Iron, from the county
of Cornwall." By the Count de Bournon. Phil. Trans., vol. xci.

i| " Analysis of the Arseniates of Copper and Iron, described in the pre-
ceding paper." By Richard Chenevix, Esa . Ibid, p. 193. [Pharmacosiderite
p. 218.]

SCORODITE. ETC. 73

re-examination of the mineral has been made by Mr. E. G. J.
Hartley, in the Oxford Mineralogical Laboratory ;* and from his
analyses it appears that potash is an essential constituent of the
mineral, though it may be present in only small quantity. Mr.
Hartley has observed that if a green crystal of pharmacosiderite be
placed for a few minutes in a solution of ammonia, its colour changes
to red, but is restored to green by the action of dilute hydrochloric
acid.

Scorodit'.; etc. (Xo.s. 5:57 to 541).

Another arsenate of iron has been called Scorodite, in consequence
of the garlic-like odour of arsenic, emitted by the mineral on ex-
posure to heat (ukij/woiiv, skorodon, garlic). In No. 5-J7 the two
arsenates, pharmacosiderite and scorodite, are seated together on
the gozzan of Wheal Borland. The two minerals, though allied
chemically, present marked physical differences ; for whilst the one
occurs in dark green cubes the other forms pale bluish-green trans-
lucent crystals, belonging to the orthorhombic system, and usually
aggregated in small globular groups, with a diverging structure.
Scorodite was regarded by the older mineralogists as an arsenate of
copper — a pardonable enough error, due to its colour and to its
occurrence, with copper arsenates in the St. Day district. Cornish
specimens sometimes show the scorodite on a matrix containing mis-
pickel, and this association at once discloses the genesis of the
mineral. Simple oxidation and hydration of the arsenide might
readily result in the formation of scorodite.

Scorodite occurs as a deposit from several of the hot springs and
geysers of the Yellowstone Park, forming in some cases a brilliant
green incrustation on the siliceous sinter. In this form the scorodite
is a very unstable substance, readily undergoing decomposition and
leaving an ochreous residue which contains more or less arsenic
acid.f

The rare species Liskeardite. from near Liskeard, described by
Prof. N. S. Maskelyne,j is representedby a single specimen No. 541.
The mineral is a hydrated arsenate of aluminium and iron, and
occurs at Marke Valley as an incrustation, associated with scorodite
and mispickel — two minerals which suggest its origin and relation-
ship.

Cronstedtite (Xos. 512 to 544).

Several examples of the rare mineral Cronstedtite are here ex-
hibited from Wheal Jane, near Truro, where the conditions of its
occurrence, judging from the specimens, are similar to those under
which the vivianite and ludlamite occur (p. 70).

* Min. Mag., vol. xii. (1900), p. 152.

•f- " Notes on the Deposition of Scorodite from Arsenical Waters in the
Yellowstone National Park." By Arnold Hague. Am. Journ. Sc, [3]
vol. xxxiv. (1887), p. 171. Journ. Chem. Soc, vol. liv. (1888), p. 122.

+ Nature, vol. xviii. (1878), p. 426. Journ. Chem. Soc, vol xliii. (1883), p. 140

74 MINERALS OF CORNWALL AND DEVON.

Cronstedtite — a mineral which borrows its name from a Swedish
chemist, Axel Frederic Cronstedt (6. 1722, d. 1765) — may be re-
garded as a hydrous ferroso -ferric silicate. It occurs in small black
lustrous crystals, referable to the hexagonal system, and remark-
able for the hemimorphism which they frequently present — the
two extremities of the crystals having dissimilar terminations.
In the specimens here shown, the mineral is mostly in radiating
groups of acicular crystals, rather suggestive of schorl, but the
substance is much softer. In No. 542 the little slender crystals
are disposed in stellate aggregates, after the fashion of some schorl,
and these repose on chalybite, which itself is spread over pyrite,
at the expense of which it has evidently been formed. In No.
543 the stellate cronstedtite is associated with chalybite and a little
limonite on pyrite. No. 544 shows a veinstone with copper pyrites
and zinc blende ; and in a vug or cavity in this stone minerals have
crystallised in the following succession — (1) quartz, (2) chalybite,
(3) cronstedtite.*

* On the chemical and crystallographic characters of cronstedtite, see
" Mineralogical Notices." By Prof. N. Story-Maskelyne and Dr. Walter
Plight. Journ. Chem. Soc, [2] vol. ix. (1871), p. 9.

NI< KEL AND COHALT-OP.ES. I r >

CASE V.

DIVISION 1.
MINERALS OF CORNWALL AND DEVON.
Minerals of the Rarer Metals.
(Nos. ."45 to <U2.)

The group of specimens exhibited in the first division of Case V.
consists of minerals which contain some of the rarer metals of Corn-
wall and Devon. It is true that the minerals containing silver and
antimony, which might fairly take a place here, are exhibited in
Case III. by side of the lead-ores, but this is an arrangement due
chiefly to convenience of space, though at the same time it is an
arrangement which does no violence to the natural relationship
of these minerals. On the other hand, manganese, which is con-
veniently represented in the case now under description, is perhaps
hardly entitled to be regarded as a rare metal ; yet the ores of
manganese are by no means common among Cornish minerals.

An easy transition is effected from the iron-bearing minerals in
the last case (No. TV.) to the rarer minerals, now to be described,
through the group of nickel and cobalt ores, inasmuch as the two
metals which thev contain bear very close relationship to iron.

Xiclel and Cobalt Minerals (Not. ~A~> to 548).

The metals nickel and cobalt are found chiefly in the natural
condition of arsenides and sulphides, but such minerals are far from
common in the West of England. They occur occasionally in the
copper- and tin lodes, especially the former, and also in cross-courses,
usually near their intersection with the east-and-west veins. Nickel
and cobalt are so closely related that they are often associated in
the same ore, and the respective minerals are not always readily
distinguished from each other by cursory inspection. On weather-
ing, however, the arsenides give rise to arsenates, and are then
readily distinguished, since the alteration-product, or " bloom," of
the cobalt ore is pink, or peach-blossom tinted, whilst that of the
nickel ore presents a peculiar green colour.

Pentlandite (No. ">45) is an iron-nickel sulphide, or nickeliferous
pyrites, which was found at one time in some quantity at Wheal
Jane, a lead mine near Truro. Niccolite (No. 546), often known by
its old German name Kupfernickel, is a nickel arsenide, distinguished
by its pale coppery red colour. It was formerly raised at the Pen-
gelly Mine, in St. Ewe. Chloamthite is an arsenide of nickel with

70 MINERALS OF CORNWALL AND DEVON.

cobalt, whilst smaltine, or smaltite, is an arsenide of cobalt with
nickel, iron being usually present in both minerals. The specimen
of smaltine (No. 547) is from Wheal Sparnon, near Redruth.

Among these cobalt and nickel-bearing minerals the most attrac-
tive to the eye is the Eryihrite (No. 548), which is a hydrated
arsenate of cobalt, resulting from the alteration of arsenical cobalt
ores, on which it usually appears as an incrustation of a peach-
blossom colour, deepening in some specimens into crimson. Crystals
belonging to the monoclinic system, are not unknown, but most
erythyrite is found as an earthy or pulverulent material, often
termed cobalt-bloom.

Manganese Minerals (Nos. 549 to 568).

Manganese is a metal closely related to iron, and rather widely
distributed in nature, though deposits of its ores are not commonly
of great magnitude in the West of England. They occur chiefly
in lenticular masses and irregular pockets in Devonian and Carboni-
ferous strata, but not usually in persistent veins. At the Restormel
Royal Iron Mine, near Lostwithiel, manganese minerals occurred
in association with the iron-ores, but only in very subordinate
quantity. Most of the ore-bodies containing manganese are found
on the north coast of Cornwall and in the eastern part of the county,
especially near Launceston ; or in the adjacent part of
Devonshire, near Tavistock, and again on the eastern side of Dart-
moor, north of Exeter. One of the finest deposits was that formerly
worked at Upton Pyne, where the ore was first raised about the
year 1770. The same vein was also extensively worked at Newton
St.Cyres, but the workings at both places were discontinued about
1810 or soon afterwards.*

Manganese occurs generally in the form of an oxide, which appears
to have been deposited from solution, in some cases as a direct
precipitate, in others through the intermediate stage of carbonate.
The original source of the metal is probably to be sought in the
crystalline rocks, where it occurs in many of the constituent min-
erals, like augite and hornblende, though usually in only small pro-
portion. If the manganese be present as silicate, it may be readily
dissolved by water containing carbonic acid, and be then held
in solution as bi-carbonate. On exposure to oxidising influences,
the neutral carbonate tends to pass into the state of a hydrated
oxide. Manganous carbonate is, however, more stable than ferrous
carbonate, and consequently in a mixture containing the two car-
bonates—and they often occur in association — the iron will oxidise
first.

It has frequently been observed that in deposits containing ores
of both manganese and iron, the manganese diminishes in depth
while the iron increases. This is explicable on the assumption
that a solution containing carbonates of both metals, rising from

* De la Beche's Report on Cornwall, etc., p. 609,

MAXOAXESE ORES. 77

below, suffered oxidation as it approached the surface. From
the experiments of M. Channissy, of the manganese mines of Rom-
aneche, it appears that from an acid solution of the salts of mangan-
ese and iron the effect of a base is to precipitate ferric oxide at first.
and that manganese dioxide is not thrown down until lon» after-
wards. Hence the upper part of a deposit of mixed ore is likely
to be the richest in manganese.* Indeed if the oxidising influence-
are not very powerful, the manganese may remain as carbonate
v* hilst the iron forms a hydrate.

Manganite and other Oxides (Xos. 549 to 564).

The characters of manganite, or grey oxide of manganese, sue well
illustrated by the specimens Xos. 549 to 562. The mineral is seen
in dark steel-grey crystals, belonging to the orthorhombic system,
usually in prisms with deep vertical striations. It is a hydrated
sesquioxide, related in composition and crystallisation to the corre-
sponding iron-mineral gothite.

Pyrolutde. or black oxide of manganese (Xos. 553 to 556). is a very
soft mineral, soiling the fingers, and usually occurring in compact
or reniform masses, sometimes with fibrous structure. It is gener-
ally a secondary mineral, resulting from the dehydration of man-
ganite or from the alteration of the carbonate. When in crvstals,
which seem generally to be pseudomorphs after manganite, the
manganese dioxide is termed poliarti>'.-\

Psilomelane is a compact black mineral, nevpr crystallised, but
usually occurring in botryoidal masses, like Xos. 557 and 560, or
in stalactitic forms, as shown in Xos. 561 to 504. The surface is
smooth with sub-metallic lustre, or sometimes velvety. Restormel
Royal Iron Mine yielded most of the specimens exhibited here
Psilomelane is a hydrated oxide of manganese, of variable composi-
tion, frequently impure, and containing barium, etc.

Manganese Carbonate and Silicate (Xos. 565 to 56*).

Dialogite, or native manganous carbonate, is here represented
by a Cornish specimen, showing the beautiful rose-red colour which
has earned for this species the name of Rhodochrosite — a name
now frequently employed. The crystalline structure is also well
illustrated by this specimen, and from this sparry character it is
known as rose spar or manganese spar. The mineral crystallises
in the rhombohedral system, and is isomorphous with calcite and
chalybite. In Xo. 566 the dialogite appears in globular masses
of a dark reddish brown colour, with a velvety surface. The colour
here may be referred to the presence of iron.

Anothe,! manganese mineral of pink or rose-red colour, something
like the carbonate but much harder, is the silicate known as

* " Traifri des Gites mineraux et metalliferes." Par Ed. Fuehs et
L. de Lauaay. Paris, 1893, vol. ii, p. 8.
t See Lacroix's " Mine'ralogie de la France," voL iii, 1901, pp. 235, 354.

78 MINERALS OF CORNWALL AND DEVON.

Rhodonite (No. 567). The specimen here shown is from Black
Down, near Tavistock, in Devonshire. The pink silicate is associ-
ated with black oxide, a not infrequent occurrence, since all man-
ganous compounds are prone to pass into a higher state of oxidation,
with production of black oxides. In Siberia, the rhodonite is some-
times cut and polished as an ornamental stone, and in this case the
black alteration-products contrast strikingly with the original red
mineral.

No. 568 is a specimen of Penwithite, described by Mr. J. H.
Collins as a hydrated silicate of manganese.* The mineral was
found at Wheal Owles, in St. Just-in-Penwith, whence the specific
name.

The ores of manganese, chiefly pyrolusite, have considerable
economic interest, being used in the production of certain alloys of
iron, and in the preparation of bleaching-powder, etc. Pyrolusite
is also employed as a source of oxygen, whence its value as a
decolourising agent in glass-making.

Bismuth minerals (Nos. 569 to 584).

Minerals containing bismuth are by no means common in the West
of England, but are occasionally found in tin-lodes, and especially
in association with ores of cobalt and nickel. Borlase statesf that in
1755 it was found by a certain Dr. Schlosser that ores containing
bismuth, with cobalt, were being thrown away at a mine in Gwennap,
and he consequently devised means for saving and separating them.
Native bismuth was at one time rather plentiful at Botallack.
According to the late Mr. Garby, " masses of some pounds weight
have been found in the soil, in the vicinity of Redruth. "J The
metal crystallises in the rhombohedral system, and is often found in
crystalline masses, with a platy structure, due to perfect basal
cleavage. Lamellar masses of notable size have been found at the
Consolidated Mines, St. Ives. The metal presents a tin-white colour,
with a suspicion of red, as shown in Nos. 569 to 572. It is extremely
fusible, so that miners roughly test an ore for bismuth by observing
whether it fuses when placed on a heated shovel. §

Bismuth is one of the small group of brittle metals, including
arsenic and antimony, and it is notable that the native bismuth
frequently contains traces of both these metals.

Native bismuth is probably a mineral of secondary origin ; and it
has been suggested by von Fritsch that it may in some cases have
been deposited from solutions by electrolytic action.il

* Min. Mag., vol. ii. (1879), p. 91 ; vol. iii. (1880), p. 89.

\ " The Natural History of Cornwall." By William Borlase, Oxford,
1758, p. 131.

t Trans. R. a ail. Soc. Corn., vol. vii. (1865), p. 86.

§ Collins's " Mineralogy of Cornwall," p. 16.

|| " Ueber die Mitwirkung elektrisoher Strome bei der Bildung einiger
Mineralien." K. von Fritsche. Dissert. GSttingen, 1862.

PITCHBLENDE. 79

The trisulphide of bismuth occurs native, forming the mineral
known as Bismuth glance, or bismuthite or bismuthinite (Xos. 573 to
581). Like stibnite, to which it is chemically related, it crystal-
lises in the orthorhombic system, and is usually found in acicular
crystals. These needles, well seen in most of the specimens
exhibited here, have a tin-white or lead-grey colour, with metallic
lustre ; but the surface is often obscured by a tarnish, sometimes
slightly iridescent. In some specimens, the mineral assumes a
filamentous or capillary form, and some beautifully delicate tufts of
brown fibres are seen in Xos. 578 and 57',». In Xo. 578 these hair-like
crystals are associated with cubes of almost colourless fluor-spar.
The association with this spar is also seen in Xo. 581.

It is probable that the sulphide represents the original form in
which the bismuth was introduced into the vein ; and the frequent
presence of fluorite as a companion suggests that fluorine may have
beeD active at the same time.

Bismite, or bismuth ochre, is a yellow or brown earthy oxide, result-
ing from the alteration of native bismuth and bismuth glance, as
seen on specimens Xos. 582 to 584.

Pitchblende (Nos. 585 to 587).

Occurring usually as a black massive substance, without any strik-
ing individuality, this mineral was mistaken by the early mineral-
ogists for other substances, such as certain ores of zinc and iron. Its
pitch-like appearance and its deceptive characters led to the trivial
name of pitchblende — a name which still clings to the mineral, even
in scientific writings. In 1780 Klaproth showed that pitchblende
contained a distinctive metal, previously unrecognised ; and as
Herschel had just then discovered the planet Uranus, the new metal
was rather fancifully named Uranium. From the presence of tins
metal, the pitchblende was called by Haidinger Uranin — a word
whjcli was modified by J. D. Dana as uraninite.

Uraninite, or pitchblende, was formerly regarded as an impure
oxide of uranium, and it does indeed contain a large proportion,
exceeding in some cases 80 per cent., of U 3 8 . This may be present
as uranous and uranic oxides (respectively containing U0 2 and UOJ,
whence the mineral was considered at one time to be a proto-peroxide
of uranium. It is sometimes described as a uranate of uranyl.
Modern research, however, has shown that it is a substance of
great complexity, containing lead, bismuth, barium and various rare
elements. Most varieties of pitchblende contain thorium or
zirconium, and certain metals of the lanthanum and yttrium groups.

The chemical composition of uraninite has been elaborately
investigated by Dr. Hillebrand, of the Geological Survey of the
United States. In the course of his analysis he obtained, by boiling
the mineral with weak sulphuric acid, a gas which was regarded as
nitrogen.* After the discovery of argon by Lord Kayleigh and Sir

* " On the occurrence of nitrogen in Uraninite." Bull. U.S. Geolog. Surv.
No. 78, 1889.

80 MINERALS OF CORNWALL AND DEVON.

W. Ramsay, it was suggested by Prof. Miers that the pitchblende gas
should be examined. This examination led Ramsay to the discovery
of terrestrial helium. He found that the gas evolved from cleveite,
a Norwegian variety of pitchblende, when examined spectroscopic-
ally, yielded a characteristic line which had been observed in the
solar chromosphere by Sir Norman Lockyer as far back as 1868,
and referred to a hypothetical element provisionally termed
helium.* The Cornish pitchblende yields only a very small
amount of this gaseous body.

Great interest has attached to pitchblende in recent years by
reason of itc remarkable radio-activity. The property of emitting
what are called Becquerel rays was known to be possessed by the
metals uranium and thorium, but the investigations of Madame
Curie, of Paris, showed that pitchblende was more active than either
of these metals. In order to explain this unexpected behaviour she
assumed that the mineral must contain some other element of
intense radio-activity — an assumption which was confirmed, after a
long course of laborious and delicate research, by the discovery of
Radium.

It is interesting to note that the three elements which have the
highest atomic weights are the three radio-active bodies which occur
associated, with others, in pitchblende, namely : —

Uranium, atomic weightf - - - 238.5

Thorium, „ - 232.5

Radium, „ ... 225

Evidence has been obtained by M. and Mme. Curie, working with
M. Bemont, of the existence of another substance of high radio-
activity, described as a new ' element ' under the name of polonium ;
whilst a third new element has been announced by M. Debierne
under the name of actinium. In preparing compounds of these
bodies from pitchblende, it is found that the radium associates itself
with barium, the polonium with bismuth, and the actinium with
the rare earths. Yet another substance of great radio-activity
has been obtained from pitchblende by M. Marckwald, who has
described it as radio-tellurium ; but it is suggested that this may
be a form of polonium.

None of these newly-discovered substances occurs in pitchblende
in more than infinitesimal proportion. Of radium, which is the best
known and probably the most abundant, it is estimated that only
about three grains are contained in a ton of the richest pitchblende.

The occurrence of pitchblende has been recorded from a number
of Cornish localities, but it is rarely found in large quantity. Dr.
Richard Pearce, in describing its discovery some years ago at Wheal

* " On a gas showing the spectrum of Helium." By William Ramsay.
Proc. Roy. Soc, vol. lviii. (1895), p. 65 ; also p. 81, and vol. lix., p. 325. '■ On
the new gas obtained from Uraninite." By J. Norman Lockyer, C.B.
Ibid., vol. lviii., p. 67 ; also pp. 113, 116, 192, 193 ; and vol. lix., p. 342.

t International Atomic Weights (0 = 16.) Journ. Chem. Soc, vol. lxxtxii
(1902.)

URAMUM-UKE.- - . S'J

Owles, in St. Just, pointed out that the Cornish pitchblende usuallv
occurs in association with other rare minerals — at St. Austell Consols
with nickel- and cobalt- ores ; at Dolcoath with native bismuth
and arsenical cobalt ; at South Tresavean with kupfemickel, native
silver and rich argentiferous gozzan. The uranium minerals seem
to occur mostly in small cross- veins. *

In recent years uranium- ores have been successfully worked at
Grampound Road, in the parish of St. Stephens, in West Cornwall—
at a mine formerly worked for tin, under the name of South Terras.
An abundant development of gozzan near the surface yielded a
mixture of earthy minerals, variable in composition, containing
uranium chiefly in the form of cupro-uranite and calco-uranite.
These ores gave way below the 10-fathom level to pitchblende— the
mineral from which they had evidently been derived. The pitch-
blende occurred in a quartz veinstone, associated with much oxide
of iron and with occasional bunches of copper ore and argentiferous
galena.

According to Mr. B. Kitto the uranium ores occurred in a vein
about three feet wide, coursing through killas in a north and south
direction. The ores were formerly treated by him, and converted
into ' orange ' and ' yellow oxide,' most of which was sent to
Germany. Uranium compounds are used in porcelain painting, in
photography, and in the manufacture of the greenish yellow uranium
glass, well known for its fluorescence. It has also been proposed
to employ uranium in steel manufacture.

In 1901 the mines at Grampound produced seventy-nine tons
of uranium ore, valued at the mine at £2,923. t The mines have
since been closed, but will probably be re-opened with the view of
supplying material as a source of radium.

The uranium mines have been recently visited by Mr. Clement
Reid, in the course of his official work on the Geological Survey.
It appears that there are at least two parallel veins, representing
cross-courses ; and the ore is found to be associated with much
magnetite and garnet. Mr. Reid has observed that these veins
carry a green garnet, which seems to be grossularia — a mineral
which it is believed has not been previously recorded from Cornwall.

Xo. 588 is a specimen of Zippeite from Wheal Edward, St. Just.
Evidently resulting from the direct or indirect alteration of pitch-
blende, it appears as a delicate canary-yellow incrustation, with a
fibro-scaly structure. With other products of the decomposition
of uranium ores, both oxides and sulphates, the zippeite is some-
times known as uranium-ochre.

Uranite {Nos. 589 to 008).
Two minerals have been included under the general name of
TJranite. Both contain hydrated phosphate of uranium, but in the

* " Note on Pitchblende in Cornwall." By Richard Pearce. Trans. Roy.
Oeol. Soc. Corn., vol. ix., p. 103.

•j- " Mineral Statistics." Home Office Pveport for 1901 (1902), p. 271.

7882. O

\*.

82 MINERALS OP CORNWALL AND DEVON.

one case the uranium is associated with copper, in the other with
calcium. Hence two species are recognised, known respectively
as Cwpro-uranite, or copper-uranite, and Calco-uranite, ovlime-ur unite.
The former is a green mineral, the latter yellow. Although they
?eem to agree in the character of their crystallisation, the copper-
bearing mineral belongs to the tetragonal system, whilst the lime
species is now known to be orthorhombic.

Cornwall is famous for its fine specimens of cupro-uranite, of which
many beautiful examples are here exhibited (Nos. 589 to 604). The
vivid green colour, the brilliant lustre, the characteristic habit of
the crystals and their associations are fully illustrated. The mineral
is generally in thin plates, square or octagonal, sometimes curved,
and always very fragile ; whilst occasionally it appears in rather
stout, square, tabular crystals, bearing pyramidal faces at the
edges, and exhibiting a perfect basal cleavage. This cleavage is
apt to impart a micaceous structure to the mineral, whence it
was formerly known as uranium mica.

As far back as 1815 the Cornish uranite was examined by William
Phillips, who figured a large series of crystals.* At that time the
mineral was regarded as an oxide of uranium.

Many of the fine old Cornish specimens were obtained from the
copper-mine of Gunnislike, near Callington, where they occurred
in gozzan at as great a depth as 90 fathoms from the surface. Nos.
589 and 590 show the curved platy crystalline masses from this
locality, whilst No. 597, also from Gunnislake, shows them spread
out in plumose form on a veinstone of quartz with oxide of iron
associated with oxide of manganese.

In other specimens, such as Nos. 601 and 602, the crystals are
seated on a brown cavernous matrix of gossan. Uranite appears in
some cases to be connected with the kaolinisation of felspar ; and
in Nos. 594 and 595, from near Redruth, the uranium mineral is seen
on altered granite, the brilliant emerald-green crystals forming
a striking contrast with the dead white matrix. At Stenna Gwynn
the mineral is associated with fluellite.

According to Mr. J. H. Collins, uranite is so widely distributed
in Cornwall that it occurs " in the shallow parts of almost every
copper-mine in the county. "f In connection with the self-lumin-
osity of radio-active bodies, it may be worth recalling the observa-
tion of the late Mr. Garby that the specimens of uranite " when
first discovered by the miners in Huel Buller and Huel Basset were
very phosphorescent — so much so that after the lights were ex-
tinguished many of the crystals might be discovered in situ."l

The observations of Madame Curie have shown, as might be
expected, that both the copper- and the lime- uranites are radio-

* " On the Oxyd of Uranium, the production of Cornwall, together with a
description and series of its Crystalline forms." Trans. Oeol. Soc., vol. iii.,
p. 112.

f Journ. Roy. Inst. Cornwall, vol. xii. (1895), p. 52.

J Trans. Roy. Geolog. Soc, Corn., vol. vii. (1865), p. 86. , '

URANITE AND CHURCHITE. H/\

active; and though not so active generally as most pitchblendes
they are yet more powerful than metallic uranium.*

Torberite, a name by which cupro-uranite is sometimes known,
was given to the mineral by Werner, in honour of the Swedish
chemist, Torber Bergmann. As his Christian name was latinised
as Torbernus, the mineral name is preferably written Torbernite.t
Chalcolite is another name given to the mineral, but it is apt to be
confused with Chalcocite, a name frequently applied to copper
glance.

The lime-uranite, known also from a French locality as Autunite.
is less common than the copper-uranite, and usually occurs in yellow
or pale yellowish-green crystals, as seen in specimens Nos. 605 to 60*.
No. 605 shows the intimate association of torbernite and
autunite.

Some of the Cornish autunite has been analysed by Prof.
Church. J

It has been suggested by M. Bourgeois that if water charged with
sulphuric acid from decomposing pyrites should flow over pitch-
blende with copper phosphates or with apatite, it might give rise in
the former case to torbernite, and in the latter to autunite — a view
supported by the synthetic researches of Debray and Winkler,
which show the possibility of the required reactions. §

Churchite (Nos. 609 to 612).

In 1865 Prof. A. H. Church announced the discovery of cerium
for the first time in this country. He found it in a mineral investing
quartz and killas, from a Cornish copper lode.|| The mineral
proved to be essentially a hydrous phosphate of cerium ; and Mr.
Creville Williams, who called attention to the presence of didy-
mium, as indicated by means of the spectroscope, suggested that
the mineral should be named after its discoverer Churchite.*^ No.
612 is interesting as being part of the original specimen analysed by
Prof. Church, by whom it was presented to the Museum. The
presence of cerium has since been detected by Church in several
Cornish apatites.

* " Radio-active Substances," a Translation of Madame Curie's Thesis.
Chem. News, vol. lxxxviii. (1903), p. 99.

f " On Mineralogioal Nomenclature." By J. D. Dana. Am. Journ.
8c. [2], vol. xliv. (1867), p. 147.

t " On the Composition of Autunite." Journ. Chem. Soc. [2], vol. xiii.
(1875), p. 109.

§ Bull. Min. Soc. Fr., vol. xxi. (1898), p. 32.

j| " Preliminary Note on a new British Mineral, containing cerium." Chem
News, 15th Sept., 1865, p. 121. Also Journ. Chem. Soc. [2], vol. iii. (1865),
p. 259.

* " On the presence of Didymium in Churchite." Chem. News, 20th Oct.,
180.3, p. 183.

78S2. G 2

84 MINERALS OF CORNWALL AND DEVON.

DIVISION 2.
MINERALS OF CORNWALL AND DEVON.

The Spars oe the Mineral Veins.
(Nos. 613 to 690).

All the crystalline minerals which occur in veins, but contain
either no metal or only some of the rarer and lighter metals, and
which never present a metallic aspect, are conveniently, though
rather loosely, grouped together under the popular name of " spars."
It is true that the rhombohedral carbonates, which are typical spars,
may contain some of the heavy metals and may even be used as ores,
so that we speak of the sparry ores of iron, manganese and zinc.
But apart from these carbonates, the term is restricted to such
minerals as accompany the ores in the form of matrix, gangue,
veinstone or lode-stuff, and which are generally regarded as non-
metallic or earthy and almost useless.*

Useless as they may be to the miner, they are of the first import-
ance to the student of mineralogy, inasmuch as they frequently
crystallise in forms of much beauty and great scientific interest,
whilst their study tends in many cases to throw light on the nature
and origin of vein-formations The principal sparry minerals in the
mines of Cornwall and Devon are quartz and fluorspar, with calcite
and barytes in subordinate quantity.

In some cases these sparry minerals form small veins, or strings,
unaccompanied by any metallif erous mineral, but in most cases they
occur in association with more or less ore, the association being often
so intimate as to lead to the inference that both matrix and ore must
have been introduced into the vein under similar conditions. It is
evident that in many cases the mineral matter has been
deposited in the cracks of the rocks from a state of solution. Such
fissures may be due partly perhaps to the contraction of eruptive
rocks on cooling or of sedimentary rocks on consolidation, partly to
disruption consequent on the intrusion of igneous matter, or in con-
nection with wider earth movements which have affected large areas
of the earth's crust. Mineral veins often run along fault planes.

Whatever the origin of these rock fissures, they would form easy
channels through which waters could circulate, bringing with them
mineral matter in a state of solution. Solution is usually, though
not invariably, facilitated by increase of temperature and of pressure,
so that solvents will generally be more effective at great depths than
near the surface. A solution, as it travels upwards, along the natural
conduit, will be gradually reduced in temperature and relieved of
pressure, so that it will become less competent to carry its freight

* Against the use of the word " gangue " see Sir C. Le Neve Foster's
remarks in his "Ore and Stone Mining," p. 11. The term " veinstone " is rather
ambiguous, since itis employed by some writers to denote the whole contents
of tiie vein, both matrix arid ore ; whilst others restrict it to the gangue-
minerals, or '' waste."

PLUG RITE. 85

of dissolved mineral matter, some of which may consequently be
precipitated on the walls of the fissure. The circulating water may
have come originally from surface -drainage, and if so will be simply
on its return-path, but it is returning charged with more or less
mineral matter which it has dissolved during its subterranean
sojourn. Solution is more active below, precipitation more active
above.

There is not unreasonably a tendency to regard the warm springs,
which are sometimes cut in a mine, as surviving representatives of
such activities as may have been potent in the deposition of the
mineral contents of a vein. It is true that Mr. Henwood remarked
that some of the warmest streams he had examined had been from
very unproductive lodes. But this obviously does not exclude
thermal waters from having been instrumental in depositing the
non-metallic veinstuff, or even metallic minerals at former geological
periods.

Siliceous deposits containing to a limited extent certain metallic
sulphides, and therefore representing true mineral veins, have been
observed in course of formation from thermal waters at Steamboat
Springs, Nevada ; at Sulphur Bank, California ; and at Boulder Hot
Springs, Montana.*

The minerals deposited from solution may be either compact or
crystalline in texture ; and if the solution should stagnate in a sub-
terranean cavity the dissolved matter may very slowly be precipi-
tated, and thus form distinct crystals. Large and fine crystals are
generally deposited with extreme slowness. Most of the beautiful
crystals exhibited in this collection have been obtained from the
walls of fissures, or cavities called vugs in the veinstone, where the
conditions must have been exceptionally favourable for crystallisa-
tion. A vein-fissure representing a plane of weakness m the rock
may have opened again and again ; and, offering each time a ready
conduit for the circulation of mineral solutions, may have received
successive deposits in the course of the history of the lode.

The second division of Case V. is devoted to a fine series of speci-
mens of fluorspar, whilst the other principal spars — quartz, calcite
and barytes — are grouped together in the first division of
Case VI.

Fluorite (Nos. 613 to 690).

Since it is believed that the Cornish tinstone has been formed from
a tin fluoride, it might reasonably be supposed that fluorspar, the
commonest of all natural compounds of fluorine, would be frequently
found in tin-lodes. Examples of the association of cassiterite and
fluorite are shown in Case I. and have been noticed at p. 26. As a
matter of fact, however, the Cornish tin-ore is not so commonly

* See J. Arthur Phillips, Phil. Mag., vol. xxxvi. (1868), p. 321 ; and '' Ore
Deposits," 2nd ed., p. 115. The Boulder Springs have been described by
Mr. W. H. Weed.

86 MINERALS OF OOfiNWALL >' Km >"'■""

accompanied by fluorite, at any rate macroscopically, as might be
assumed. This paucity of fluor, which is a calcium fluoride, may be
connected with the general scarcity of calcareous matter in the tin
districts of Western Cornwall. In the copper-lodes, however, and
yet more notably in the lead-veins, fluorspar is common. This is
especially marked in the lead district near Liskeard, where calcite is
also a characteristic mineral. Many of the fine specimens of fluorite
in this collection are from the lead-lodes of Eastern Cornwall and
Western Devon.

The mineral known as Fluorite, fluorspar, or simply fluor, and often,
termed by Cornish miners cann, is a fluoride of calcium, crystallising
in the cubic or regular system. Sharply defined cubes, often of
large size, are very common : witness such examples as Nos. 613,
618, 622, 678, and 681. A little to the left of this collection stands a
Pedestal Case, opposite Wall Case 18, which contains some cubic
crystals of fluorite, each measuring more than a foot along the edge.
In this specimen, from Wheal Mary Ann at Menheniot, the cubes are
of deep blue colour, and certain faces are partially coated with a
deposit of pyrites. It is notable that these gigantic cubes are built
up of an aggregation of smaller cubes, or sub-individuals.

Octahedral crystals are rare in British fluors. No. 648 shows a
combination of the octahedron and cube, whilst No. 668, from
Beer Alston in Devon, has the general form of an octahedron, but
is a polysynthetic structure made up of aggregated cubes. Yet
whatever the external shape of the crystal, fluorite always presents
a perfect cleavage parallel to planes of the regular octahedron.
The direction of cleavage is so marked in No. 621, that although
the cubic crystals maintain their integrity, it is evident that a very
slight shock would detach from each three-faced solid angle, or
quoin, a tetrahedron which would leave an equilateral triangle
representing the face of an octahedron. In like manner the octa-
hedral planes of cleavage are visible in the cracks which run across
the translucent quoins of the huge blue cubes in the adjacent case
opposite Wall Case 18.

The four-faced cube, known technically as the tetrakis-hexa-
hedron, a kind of cube which seems to carry upon each of its faces
a four-sided pyramid, is so characteristic of fluorite that it has been
called the fluoroid. Sometimes it occurs alone, as in the little
violet crystals on No 647, but usually it is found in combination
with the cube. Thus, in Nos. 638, 649, 650, 651, not to mention
others, the twelve edges of the cube are in each specimen bevelled
by the planes of the four-faced cube. Most of these specimens
come from St. Agnes, and it is notable that the faces of the tetrakis-
hexahedron are, in some cases, rough and corroded whilst the faces
of the cube remain brilliant.

H It often happens that the faces of a cube of fluor, instead of being
quite^plane, show markings which represent a very low square pyra-
mid, as may be distinctly seen on No. 621. These facets are known
as vicinal faces, and possess much significance to the crystallo-
grapher.

Another form not infrequently found on crystals of Cornish
fluorite is the six-faced octahedron, or hexakis-octahedron. The
faces of this form replace the solid angles of the cube, as is clearly
shown in the fine specimens of yellow and blue fluor from Wheal
Mary Ann, Menheniot, such as Nos. 615, G22, and 623. Thus, in
Xo. 622, which is part of a large cube of blue fluor, the three-faced
solid angle is replaced by six planes, which if repeated on all the
cube-quoins would constitute the perfect forty-eight-sided form.
It will be noted that these corner faces are rough, and this led to
the suggestion when such crystals were discovered many years ago,
near Liskeard, that the triangular faces might have been artificially
filed, but it became evident, on close examination, that the modifica-
tion was perfectly natural.

Other forms are not common on Cornish fluor, but occasionally
the rhombic dodecahedron is represented. On No. 654 the edges
of the cube are truncated by rough, rather rounded, inconspicuous
planes of this solid. Peculiar interest attaches to this specimen,
inasmuch as it shows an internal cube which has been coated with
pyrites, upon which more fluor has been deposited, and through
this transparent envelope the brilliant brassy pyrite is clearly visible.

Stages in the growth of a crystal may often be detected in fluor-
spar, and many of the specimens, such as Nos. 622, 631, 632, and 633,
show a zonal structure, due to a regular sequence of deposits. Bands
of colour often mark successive episodes in the history of a crystal.
Such colour-bands may be detected in many of these specimens ;
No. 633, for example, is a polished slab which shows, with exceptional
distinctness, a number of parallel stripes of vivid green colour.
The purple fluors, numbered 631 and 632. are also remarkable for
their colour-bands. In Nos. 622 and 623, deep blue zones are well
seen in the interior of pale blue cubes.

Fluorite is a mineral which displays great diversity of colour,
as seen in the specimens in this Case ; but even a greater variety
is seen in the Ludlam Collection in the Hall, where Case III. is en-
tirely given up to this polychromatic species. As this series includes
foreign specimens, it contains some which possess tints unknown
among our British fluors, such, for instance, as the beautiful pink
fluor-spar from Switzerland.

Fluor destitute of colour is quite a rarity. No. 616, from Beei
Alston, approaches the colourless condition. The dispersive power
and refractive power of fluor render the pellucid colourless mineral
of value for the construction of objectives for microscopes, as intro-
duced by Prof. Abbe. A variety from Switzerland has been applied
to this purpose. The lenses of fluor are used in conjunction with
lenses of Jena glass, so as to produce an improved kind of achro-
matic objective which is termed ' a r pochrorwitic?\

* See Prof. Miers's " Mineraloiy," 1902, p. 96.

f"Jena Glass." By Dr. H. Hovestadt. Translated and edited by
J. D. Everett, M.A., F.R.S., and Alice Everett, MA. 1902. P. 88.

88 MINERALS O? CORNWALL A^'J r^"C".

Many of the specimens exhibited in this Case show that the faces
of crystals of fluor-spar are apt to be corroded and etched to a re-
markable extent. Nos. 616, 618, 620, and 656, not to cite other
instances, clearly show the etched figures due to the action of natural
solvents. In some of the specimens from Beer Alston the edges
and solid angles have been so roughened and rounded that the cubes
show a tendency to become rather spherical, as seen in Nos. 660,
661. From the old mines of Beer Alston, between Tavistock and
Plymouth, where argentiferous galena was formerly worked on an
extensive scale, a fine suite of crystallized fluors is here exhibited,
including certain specimens of rich smalt-blue colour, and others of
pale sea-green tints, such as Nos. 657 to 668. It is notable that
while the lead mines of South Devon have yielded such fine specimens
of fluor, the old mines of silver-lead in North Devon, like Combe
Martin, were not remarkable for this mineral.

Some of the boldest crystals of fluorite shown in this case were
obtained from the lead mines formerly worked at Menheniot near
Liskeard, especially from Wheal Mary Ann. Many of these show
characteristic associations of minerals. Thus in No. 653 the fine
yellow cubes, implanted on crystalline quartz, are sprinkled over
with brilliant cubo-octahedra of pyrite. No. 669 is an instructive
specimen, showing large octahedra of pale green fluor coated with
minutely crystallized quartz, giving a white drusy surface to the
crystals, and on this surface there has been formed a second deposit
of fluor, this time in purple crystals, showing a combination of cube
and four -faced cube, and finally on this purple fluor copper-pyrites
has crystallized.

In No. 674, from near Redruth, a base of copper-pyrites having
a tarnished surface, due probably to a coating of covellite, carries
prismatic crystals of dead white quartz, associated with fluorite
in pale yellowish green cubes, having the quoins modified by planes
of the six-faced octahedron and the interior zoned with blue bands.
In No. 675, from Caradon, a matrix of green fluor is partly hidden
beneath a crop of snow white crystals of quartz, on which occurs
a second growth of green fluorite, bearing a final crystallization of
copper-pyrites.

Calcite is associated with several of the specimens of fluorite from
Menheniot. Thus, the blue cubes of fluor in No. 670 are moulded
on crystals of quartz, but carry on their surface calcite in white
crystals, consisting of obtuse rhombohedra combined with the hexa-
gonal prism. In No. 681, again, fine cubes of blue fluor are encrusted
on certain faces with quartz in small crystals, producing a drusy
surface, and on this quartz calcite has finally crystallized.

It is notable that fluorite is often pyrophosphoric, that is to say,
it becomes self-luminous on exposure to very moderate heat. The
amorphous opaque white fluor, No. 686, is remarkable for its phos-
phorescence. When slightly heated it emits a beautiful green glow,
whence the name CMorophane sometimes applied to such a variety
of fluor — whence also the term pyro-emer aid. Since this white fluor

FI.UORITE. 89

exhibits a green light, the colour of the phosphorescent glow seems
to bear no necessary relation to the colour of the mineral.

Pseudomorphs after fluorite are well known to collectors. In Nos.
687 and 688 cubes of fluor are encrusted with a deposit of quartz,
giving the crystals a drusy surface. In No. 689 the fluor has been
removed by solution, leaving a cubic hollow, in which a little chaly-
bite has crystallized. Other epimorphs, showing cube-shaped
cavities, left probably by the removal of fluor-spar, are exhibited in
Case IV. (see No. 515, p. 69).

In No. 690 from Tavistock, octahedra of pale green fluorite are
superficially replaced by opaque white chalcedonic silica, or horn-
stone. In Case VI., the specimen No. 774 shows a fine octahedron,
consisting of chalcedony which has entirely taken the place of
fluorite.

The ultimate source of much of the fluorite in the Cornish lodes
' is probably to be traced back to a very early phase in the history of
the veins. Some of the fluor may indeed have been connected with
the original formation of the tinstone. If it be admitted that the
cassiterite has been formed by the reaction of tin-fluoride and water-
vapour, it is evident that the formation of the stannic oxide would
be accompanied by the production of hydrofluoric acid. This acid
acting on lime-bearing minerals, such as certain felspathic constituents
of the granite, might produce calcium fluoride. Hence the forma-
tion of cassiterite would be accompanied or followed by the produc-
tion of fluor-spar.

It is known that fluorine, in the form of hydrofluoric acid and
fluoride of silicon, occurs among the exhalations from fumaroles,
whilst calcium fluoride and other solid substance^, containing
fluorine are found among volcanic sublimates. There is no reason
to doubt, however, that most of the fluorite from the mines of Corn-
wall and Devon has been formed by deposition from solution, pro-
bably in thermal waters. Fluorine is known to occur in certain
natural waters, notably in some of the hot springs of Galicia.
Whilst it is present in some waters as sodium fluoride, it exists in
others as calcium fluoride. Small crystals of fluor have been found
on mortar in the old Roman baths of Plombieres ; but here it was
probably derived from the fluorite which existed in the granite
through which the water passed. Glasses used at thermal springs
often acquire a dull surface, but the popular notion that this is due to
corrosion by hydrofluoric acid is not always correct.

90 MINERALS OF CORNWALL ANt.

l.'IZj V UJ' •

CASE VI,

DIVISION 1.

MINERALS OF CORNWALL AND DEVON.

The Spars of the Mineral Veins, continued.

Quartz {Nos. 691 to 718).

Of all the minerals which contribute to the formation of the vein-
stones in the West of England, Quartz is by far the most abundant. *
As it is so much harder than the other sparry minerals of the veins —
fluorite, calcite and barytes all yielding readily to the knife whilst '
quartz resists — it is sometimes termed by the miners ' hard spar ' ; or
it is referred to, in consequence of its abundance, as simply 'spar.'
Some of its general characters have already been noticed (p. 21).

Where cavities, or vugs, occur in the veinstone, the quartz will
have opportunity for free crystallisation, and the walls of these
hollows may consequently be lined with crystals. In like manner,
the sides of fissures in granitic or slaty rocks, may be studded with
crystals of quartz. It is from such situations that the fine speci-
mens here exhibited have been derived.

A crystal of quartz, when developed under favourable conditions,
usually assumes the form of a six-sided prism, attached by its base
to the veinstone or to the mother-rock, and terminated at the free
end by a six-sided pyramid. Most of the crystals in this case
exhibit such a combination of forms. In many of the specimens the
prisms are elongated along the vertical axis, producing slender
crystals, whilst in others the planes of the terminal pyramid pre-
dominate, giving rise to groups of short sharp-pointed crystals :
Nos. 695 and 696 illustrate the former, and No. 691 the latter habit.
In the quartz-porphyry of many Cornish elvans bi-pyramids of quartz
are not uncommon. In No. 693 the crystal of quartz appears to be
flattened by the development of two opposite faces of the prisms at
the expense of the others. The planes of the terminal pyramid
may be equally developed, producing regular forms like those
of No. 670 ; but it frequently happens that the pyramidal
planes are alternately large and small, as seen in No. 696, thus
suggesting that the faces are really those of two correlative rhombo-
hedra.

It is very characteristic of quartz that the prism faces are striated
transversely, that is, in a direction perpendicular to the morpho-
logical axis, as seen with great distinctness in Nos. 694 and 696.
This is due to an oscillatory combination of the prism and a pyramid.

i * Quartz is probably the most widely distributed mineral in Nature " next
to water." (Max Bauer's Lehrbuch der Mineralogie, Stuttgart : 1904.)

QUARTZ. 9.1

Most of the crystals of quartz in the series, numbered 691 to 698,
arc more or less opaque, in some cases snow-white or dead- white.
This character is common in crystals of quartz from veinstones,
whereas quartz which crystallises in the fissures of granite and slate
is often transparent, and sometimes quite pellucid. When clear
and colourless quartz is known as Rock crystal, and crystals of this
kind may be found in nests along the joints of slaty rocks in the cliffs
at Tintagel and in the Delabole quarries. Small crystals are usually
more perfect in shape and brilliant in lustre than large ones. The
limpid colourless crystals are known as Cornish diamonds.

In describing the old museum of the Royal Society, Grew wrote :
" Of our bastard diamonds here in England the Cornish are the
best."* Borlase, in his " History," describes and figures a number
of Cornish crystals of quartz, referring especially to a very fine
collection made by Mrs. Grace Percival, and preserved " in her
Fossilary " at Pendarves for the " attentive inspection of every
inquisitive Fossilist."f

Quartz sometimes assumes a brown colour, more or less pro-
nounced, and is then termed Smoky quartz. No. 707 is a beautifully
sharp and clear crystal, from Tintagel, with a faint brown tinge.
The colour of smoky quartz is often referred to the presence of
organic matter, but in some cases it is said by Weinschenk to be
due to the presence of a compound of titanium. This crystal en-
closes delicate hair-brown needles, probably of rutile, or titanium
dioxide.

In the fine example of capped quartz, No. 700, a hexagonal pyra-
mid of the mineral fits perfectly into a hollow envelope, which has
formed its cap. Between the formation of the crystal and the cap,
a thin coating of some foreign substance, like mica in some specimens
or clay in others, has been deposited, so as to interrupt the continuity
of growth and secure freedom between the original formation and its
shell.

No. 701 shows a curious form of yellowish quartz in globular
masses composed of diverging columnar crystals, which give rise, on
fracture, to a stellate appearance. Since fibrous quartz is occasionally
found in the cross-courses in Cornwall, it is known to the miners as
cross-course spar.

The so-called hacked quartz, represented by No. 703, is crystalline
quartz with apparent incisions, as though the mineral had been cut.
These hollows have been left by the disappearance of thin tabular
crystals, probably barytes, between which the quartz had been
deposited. In No. 704 from Herodsfoot Mine the crystallised quartz
forms an epimorph, having invested tabular barytes, which on
removal would leave imprints like those of hacked quartz.

The well-known Babel quartz is illustrated by No. 705, from Beer-
alston in Devonshire. Here the white crystalline quartz has been

Museum Regalis Societatis," London : 1681, p. 283.
The Natural History of Cornwall," Oxford : 1758, p. 122.

02 MINERALS OF CORNWALL A'Nu ujsvurt.

developed in little step-faced turrets, rising from a broadly extended
face of quartz, which seems to have been itself deposited on crystals
of fluor-spar, now vanished.

Amethyst, more or less pronounced in colour, is occasionally found
in the mineral- veins of Cornwall, and notable specimens have been
obtained from Wheal Uny and Wheal Tolgus, near Redruth. In
No. 708 the violet tint is pale, whilst in No. 709 it is a rich deep
colour, and in No. 710 the pigment seems so dense as to render
the crystal practically black. The colour of amethyst is commonly
referred to the presence of manganese, in the state of oxide. It is
notable that on exposure to a moderate heat the amethystine colour
is lost, and the mineral becomes greenish yellow, like the variety of
quartz known as Citrine. Much of the yellow quartz used as an
ornamental stone is simply " burnt amethyst." Veins of amethys-
tine quartz lose their colour at the outcrop, becoming first greenish
and then colourless. Sulphur has been detected in certain kinds
of amethyst, and the colouring agent has been regarded by A. Nabl
as ferric thiocyanate.*

Professor Judd has shown that amethyst usually exhibits a
lamellar structure, due to mechanical stresses, and has suggested
that quartz which has a tendency to undergo this molecular change
should be distinguished as unstable quartz.^ Such quartz presents,
on fracture, a rippled surface ; and all quartz which displays this
structure, whatever its colour, is sometimes termed, following
Brewster, amethyst. The intersection of two systems of curved
ripples or ' thumb-mark ,' may produce on the fractured face a
pattern not unlike that resulting from ' engine turning.' The un-
stable quartz has a great tendency to assume purple colours, and,
moreover, the colour is often concentrated along the lines between
the lamellae. The optical properties of amethyst have been the
subject of much study ; and it is notable that the component
lamellae in the mineral are alternately right-handed and left-handed
with regard to their action on polarised light.

Red quartz, known frequently as Eisenkiesel, owes its colour in
most cases to mechanically enclosed oxide of iron. Such iron quartz
is well illustrated, by the series Nos. 711 to 714, from the Restormel
Royal Iron Mine, near Lostwithiel. In No. 713 the rich red quartz
is associated with psilomelane, or oxide of manganese. Quartz
crystals not infrequently enclose foreign substances, such as the
specular iron-ore in No. 694.

The interesting specimen No. 715, from Cook's Kitchen, near
Camborne, shows large crystals of quartz bearing hollow epimorphs,
which are thin crusts that have taken the form of lenticular crystals
of chalybite and are themselves sprinkled over with red oxide of iron.

* Journ. C'hem. Soe., 1899 (Abstracts), p. 561.

■)■ " On the Development of a Lamellar Structure in Quartz-crystals by
mechanical means." By Prof. John W. Judd, F.R.S. Min. Mag., ^oL viii.
(1889), p. 1. Also :" Additional Notes." Ibid, vol x. (1894), p. 123.

t'ALCITK. ■■'%

Xo. 716, from Botallack, is a specimen of quartz pseudomorphous
after calcite in obtuse rhombohedra.

Many interesting associations of quartz will be observed in this
series. Some very fine bisphenoids of copper-pyrites are crystallised
on the group of prismatic crystals of quartz in Xo. 696, from Red-
ruth, whence also was obtained the next specimen (697) which
shows a somewhat similar grouping of quartz and chalcopyrite.
Excellent crystals of mispickel have seated themselves on the quartz
in Xo. 695.

The history recorded by the specimen, Xo. 698 is as follows :
opaque white quartz has crystallised on a chloritic veinstone, with
copper pyrites ; then chalcopyrite in bisphenoids, now tarnished,
has been formed on the quartz ; and finally, chalybite has been
developed, in aggregates of fish-scale crystals. In Xo. 691 sea-green
fluorspar has crystallised in bold cubes on quartz in fine hexagonal
prisms, with pyramidal terminations ; and then a secondary growth
of quartz has taken place, this time in small crystals beautifully
pellucid, and doubly terminated. In many other specimens it will
be noticed that a second crop of quartz crystals, often of small size,
has been formed on large pre-existing crystals of quartz.

Calcite (Nos. 719 to 742).

Carbonate of lime is rare in the veinstones of Cornwall, and is
practically absent where the veins run through granite. In eastern
Cornwall there is more calcareous matter than in the west, and Mr.
Collins has suggested that this " perhaps points to a former
westward extension of overlying Devonian limestones."* In the tin
lodes of the west, carbonate of lime is quite an exceptional mineral.
The specimen, Xo. 38 (Case I.), is interesting as showing wood-
tin with the laminated variety of calcite known as Schiefer spar
or " slate spar." Most of the specimens in this Case have been
obtained from the lead mines near Liskeard, especially from Herods-
foot and Wheal Wrey.

Calcite, or native carbonate of lime, crystallises in the hexagonal
system, and presents perfect cleavage parallel to the fundamental
rhombohedron. Greg and Lettsom remark that " in Cornwall and
Devonshire low hexagonal prisms and tabular forms prevail." f
This assertion is partly justified by No. 739 from Botallack, and No.
740 from Wheal Friendship, near Tavistock — the crystals in both
specimens having a tabular habit by predominance of the basal
pinacoid and only slight development of the hexagonal prism.

The beautiful white crystals from Wheal Wrey, associated in
some cases with iron pyrites in brilliant cubes, are either slender
prismatic crystal" like those in Nos. 720 to 722, or stout prisms as in
No. 724.

Careful examination will show that what looks like a hexagonal
prism is often a very acute rhombohedron, the faces not being

* Journ. Hoy. Inst. Corn., vol. xii. (1894), p. 54.

f " Manual of the Mineralogy of Great Britain, etc.," p. 36.

94 MINERALS OF CORNWALL AND DEVON.

parallel-sided. Two generations of calcite crystals may be noted
in some of the specimens, as in No. 723, where the larger crystals
are apparently impaled by the slender prisms, to which they are
therefore subsequent. In Nos. 728, 729 the calcite appears in sheaf-
like aggregates of crystals, on a base of red quartz with a thin
coating of secondary quartz and a sprinkling of pyrite. The
beautiful snow-white calcite of Herodsfoot (No. 732) in polysynthetic
crystals is likewise associated with quartz and pyrites.

In No. 741 the calcite is pink, in consequence of a little
associated iron or manganese.

Calcite, by reason of its ready solubility in carbonated waters,
is a mineral of great mobility, being easily removed from one situa-
tion and deposited in another. Waters containing sulphuric acid
from decomposed mundic will remove the lime as sulphate, and tend
to deposit it as gypsum. No. 742 is a specimen of finely crystallised
selenite from a gypseous deposit in a boiler near Kedruth, which
was fed with water containing sulphate of lime in solution.

Dolomite (Nos. 743 to 746).

Calcite is subject to some variability in chemical composition
by the replacement of its calcium to a greater or less extent by other
divalent metals, notably by magnesium. When a considerable
proportion of magnesium is present, the spar frequently displays
a pearly lustre on the faces of the crystal, whence it is known as
pearl spar. If the two carbonates be present in equal molecular
proportion, the resulting compound is the double carbonate termed
Dolomite. In specimen No. 743 the spar exhibits not only the
nacreous lustre but the characteristic curvature of the faces, the
curvature becoming so pronounced as to produce " saddle-shaped "
crystals. Here the dolomite is seated on quartz, well crystallised
and slightly amethystine in tint, and is itself sparsely sprinkled
with pyrites.

No. 744, from Menheniot, shows the following sequence of deposits
viz. : (1) quartz; (2) fluorite; (3) second growth of quartz;
(4) dolomite ; (5) pyrite. The fluor is in blue cubes ; the quartz
of the second generation is in very small clear sharp crystals ; and
the opaque white dolomite is in rhombohedra, which have their
faces slightly curved and distinctly pearly, as seen also in Nos. 743
and 745.

In No. 745, from Beer Alston, in Devon, the succession is simpler,
being (1) fluorite, (2) chalybite, and (3) dolomite. No. 746 is note-
worthy for its well-formed rhombohedra, different from the lenticular
crystals on some of the previous specimens.

Dolomite has been formed artificially in various ways : for example,
by heating carbonate of lime with a magnesian solution, such as
the bicarbonate or the chloride. Even at 100° C. dolomite may be
so formed, but a higher temperature favours the reaction. * Dolomi te

* F. Hoppe-Seyler in Zeitseh, f. Geol., vol. xxvii. (1875), p. 495.

BARYTES. 95

has also been detected as a natural precipitate from certain mineral
waters.* The subject will be again referred to.

Barytes (Nos. 747 to 758.)

Although Barytes, or sulphate of barium, is a very common mineral
in the veinstones of the north of England, it is remarkably rare
in Cornwall, even in the lead-lodes. Formerly one of the chief
localities for Cornish barytes was the mine in Gwennap called Ale
and Cakes, afterwards one of the " United Mines," and subsequently
absorbed in the Consolidated Group. Here the mineral occurred
in a copper lode, at a depth, according to Mr. Garby, of 170 fathoms
from the surface.")" Nos. 755 to 757, from this locality, show the
characteristic greenish grey colour of the crystals, and their aggrega-
tion in sheaf-like groups. The crystals tend to become darker in
colour on long exposure to light. J

Some of the silver-lead mines in the neighbourhood of Liskeard
have yielded beautiful specimens of barytes in sharply defined
crystals of yellow colour, brilliant lustre, and tabular habit ; witness
the specimens Nos. 747 to 754, from Wheal Mary Ann, in Menheniot.
Iron-pyrites occurs here in association with the barytes ; and its de-
composition may have furnished sulphuric acid to the waters of the
mine, so that on meeting a solution containing any barium salt,
the almost insoluble sulphate would be precipitated.

In No. 753 the following succession of minerals is shown : (1)
fluor-spar in sea-green cubes ; (2) quartz in white prisms ; (3) barytes
in pale brown tabular crystals. The pink barytes, No. 758, is from
Babbicombe in Devon, where it occurs in the limestone.

Further remarks concerning barytes may be conveniently deferred
until the more typical examples from other localities come under
review (pp. 168, 186).

DIVISION 2.

MINERALS OF CORNWALL AND DEVON.

Miscellaneous Minerals.

(Nos. 750 to 826).

A number of Cornish and Devon minerals which could not, with
regard to scientific propriety, be placed in any of the foregoing
classes are here grouped together as a miscellaneous assemblage,
brought into association only by their local occurrence. They form
a group with no pretence to homogeneity, either chemical or geo-
logical, including as they do such diverse minerals from such varied
formations as — wavellite from the Carboniferous shales, calcite
from the Devonian limestone, various silicates from the altered

* Comptes Rendus, vol. c. (1888), p. 665.

t Trans. Boy. Qeol. Soc. Com-, vol. vii. (1865), p. 81.

% J. H. Collins : "-Handbook," p. 13.

96 MINERALS OF CORNWALL AND DEVON,

killas, felspars from the granite, and garnets and other minerals
from the greenstones, with a few other substances obtained from
certain lodes but hardly suitable for exhibition in any of the pre-
ceding series. Although these minerals could not be appropriately
placed elsewhere, it seems necessary to exhibit them in order to bring
the collection within some reasonable approach to completeness as
representative of the mineral resources of Cornwall and Devon.

Chalcedony (Nos. 759 to 776).

Silica occasionally occurs in veins in the condition of Chalcedony,
but although this is chemically identical with quartz it could hardly
be placed by the side of that mineral, in the group of spars, inas-
much as it is not apparently crystalline, and crystalline structure
is an essential characteristic of a " spar." Instead of forming
crystals, chalcedony usually occurs in masses which are mammillary,
botryoidal, or stalactitic in form. Yet, when examined in thin
sections under the microscope, the chalcedony is seen to possess
a crystalline structure, being composed of fibres, which differ however
in optical characters from true quartz. Hence chalcedony is re-
garded as a crypto-crystalline or micro-crystalline variety of native
silica.

Very beautiful examples of stalactitic chalcedony were formerly
obtained from the Trevascus mine, in the parish of Gwinear, and
some are here exhibited which show admirably the delicate and even
fanciful shapes of the specimens from this locality (see notably Nos.
759, 760, 763, 770). Many other examples of rather similar char-
acter are shown from Pednandrea, near Redruth (Nos. 767 and 768).
These specimens sufficiently illustrate the characteristics of the
mineral — its grey yellow or brown tints, its translucency, its rather
waxy or resinous lustre, and its conchoidal fracture. It is notable
that the surface is coated in some cases with a bluish bloom, of much
delicacy and beauty, as seen on Nos. 765 and 766. Other specimens
of chalcedony, perhaps still finer, are exhibited in the Ludlam collec-
tion in the Hall, Case IV.

The forms of chalcedony at once suggest that it has been deposited
from siliceous solutions ; and it was formerly supposed that a little
opal, or soluble hydrated silica, was often associated with the fibro-
crystalline mineral, thus causing the chalcedony to have a slightly
lower density than that of quartz. In No. 772 a chalcedonic sub-
stance, scarcely, if at all, distinguishable from true flint, from the
Chalk, has been deposited in a brecciated copper-lode, with chalco-
pyrite, siderite and ' peach.'

Chalcedony sometimes forms a coating over crystals of quartz and
other minerals, as shown in Nos. 761 and 762. On the removal of
the invested mineral, the chalcedonic crust may be left as a hollow
shell, such as is seen in No. 773. Here the angular cavities in the
chalcedony represent the shape of the mineral removed, apparently
in this case fluorspar. True pseudomorphs of chalcedony are not
uncommon, and in No. 774 the mineral has assumed the form of a

CHALfKDONY. 97

fine octahedral crystal of fluor. The material of such pseudomorphs
is often described as hornslone. In some cases the fluor is simply
invested, but in others completely replaced, by the chalcedonic
mineral.

The remarkable pseudomorphs known as Haytorite (No. 775) are
composed of chalcedonic silica which has taken the form of datolite.
According to Geinitz, who examined the material microscopically,
the pseudomorphism was effected by gradual change and not by
envelopment. Datolite is a basic silicate of boron and calcium,
sometimes regarded as a boro-silicate of lime. Dr. Busz has detected
datolite with garnets, in the limestone of South Brent in Devonshire*;
but though now extremely rare as a British mineral it must have
existed in large crystals when these fine pseudomorphs were formed.
Haytorite takes its name from the locality on Dartmoor, where it was
discovered. The Haytor iron mine yielded not only haytorite, but
also pseudomorphs of chalcedony after calcite. The magnetic iron
ore of this mine has already been referred to (p. 66). Haytorite has
likewise been recorded from North Roskear Mine, in Cornwall.

Beekite (No. 776) is an orbicular form of chalcedony, named after
Dr. Beek, Dean of Bristol, who first called attention to it, as an
incrustation on fossils in South Devon. It was described by the late
Mr. W. Pengellyf and analysed by Professor Church.f Beekite
generally appears either as a deposit of silica in concentric annular
masses on corals and other fossils, or as a pseudomorphic replace-
ment of them, but it occurs also on fragments of limestone which are
not distinctly organic. Prof. T. McK. Hughes regards the beekite
as chalcedonic chert formed as a thin layer just beneath the surface
of the limestone, and revealed only on removal of the external crust :
the siliceous material then exposed may form a hollow shell so thin
as to float on water, and in some cases enclosing loose earthy matter
which rattles when shaken.§

Certain siliceous minerals more or less akin to chalcedony, but
differing generally in optical characters, have been discriminated by
the microscopic investigations of French mineralogists in recent
years, and have received distinctive names, such as lussatite, lute-
cite, quartzine and pseudo-chalcedonite.||

Opal, or hydrated silica deposited in a colloidal state as an amor-
phous mineral, less hard and less dense than quartz, is by no means
common in the West of England. No. 777 is an interesting specimen
showing opal in association with cassiterite,. This specimen from
Trumpet Consols, near Helston, was presented by the late Sir W. W.
Smyth, F.R.S., and shows the opal as a milk-white and pale blue
translucent mineral.

* Oeol. Mag., 1896, p. 492. N. Jahrb f. Min., 1899. p. 90.

t " On the Beekites found in the Red Conglomerates of Torbay." Rep-
Brit. Assoc., 1856, p. 74.

% PhU. Mag. [rv.], vol. xxiii., p. 95.

§ " On the manner of occurrence of Beekite and its bearing upon the origin
of siliceous beds of Palaeozoic age." Min. Mag., vol. viii. (1889), p. 266.

|| See Prof. Lacroix, " Mineralogie de la France," vol. iii. (1901), p. 120.

7882. II

98 MINERALS OF roRNWALL ANP DEVON.

In connection with the formation of opal, chalcedony and quartz
in mineral- veins, it may not be out of place to call attention to an
observation of Prof. Spezia, during the construction of the Simplon
tunnel through the Alps. He obtained, from a fissure in the gneiss,
a gelatinous substance, like vaseline, apparently a mechanical
mixture of silicic acid and aluminium' hydroxide, in a colloidal con-
dition. Very minute crystals of quartz were embedded in the sub-
stance, and it is suggested that this gelatinous silicic acid probably
represents a stage in the formation of quartz.*

Calrite (Nos. 778 to 783).

The specimens of Calcite here grouped together could hardly find a
place with the calcites already described from the lodes of Cornwall
and Devon, inasmuch as they were obtained not from mineral- veins,
but from limestone quarries. With the exception of No. 782, which
is a specimen from Ashburton, all the calcites here exhibited are
from the quarries near Plymouth, opened up a century ago to furnish
stone for the construction of the breakwater.

The Plymouth rag forms part of the Great Devon Limestone,
which is referable to the Middle Devonian, or Eifelian, group of
strata. Between 3,000,000 and 4,000,000 tons of limestone were
extracted for Rennie's great structure from quarries at Oreston,
about a mile from Plymouth. In the fissures of the rock, as is
common in other limestones, crystals of calcite were found. Some
of the specimens, as Nos. 778 and 779, show the crystals attached to
the mother- rock ; whilst others, like Nos. 780 and 781, exhibit the
crystals clustered around stalactites which have formed in cavities of
the limestone. Some of the specimens, notably Nos. 780 and 781,
possess a yellow colour, which has often suggested to quarrymen the
name of sugar candy spar. The colour is no doubt referable to a trace
of iron, much of the Devonian limestone being veined and clouded
with ferruginous stains.

In No. 783, from the Ilfracombe limestone, the carbonate of lime
has been deposited in a coralloidal form, and appears to be in the
condition oVAragonite. This species, though chemically identical
with calcite, is slightly denser and harder, and when crystallised
assumes forms of the orthorhombic system. (See p. 150.)

Wavellite, etc. (Nos. 784 to 790).

According to the late Mr. Townshend Hall, Wavellite was discovered
about the year 1785 by Mr. I. Hill, of Tavistock.f Sir Humphry
Davy, who examined it chemically in 1805, says, " This fossil was
found many years ago by Dr. Wavel in a quarry near Barnstaple." +

* Joum. Chem. Soc, vol. ii., 1901 (Abstracts), p. 393.

t " On the Mineral Localities of Devonshire." Trans. Devon. Assoc vol ii
Tart ii., 1868, p. 332. ' "'

+ " An Account of Some Analytical Experiments on a Mineral Production
from Devonshire." Phil. Trans, for 1805, p. 155,

FKLSFARS. ETC !l!t

It was taken at first for a zeolite, but Davy was led to regard it as a
hydrate of alumina and proposed to call it, from this false notion of
its composition, hydrargyllite, though he states that Dr. Babington
had suggested that it should be named wavellite after Dr. Wavel, of
Barnstaple. The true nature of the mineral as a hydrated phosphate
of alumina was determined by Wavel.

Wavellite occurs in black slaty rocks of the Culm-measures at
Filleigh, between Barnstaple and South Moulton, in North Devon.
As seen in Xos. 784 to 788, it forms small hemispherical masses,
composed of radiating fibres of acicular crystals, of white, grey,
brown, or bluish colour ; whilst in the narrow crevices of the rock
it spreads out in the form of circular films, with a radiate structure.
With these typical specimens from Devonshire, the visitor may
compare the Irish wavellite, represented in Case XII. The species
has also been found in Gower, in South Wales, by Mr. R. H. Tidde-
man.*

Tavistockite — a rare mineral from near Tavistock, described by
Prof. A. H. Church.f and represented by Xos. 791 to 793 — appears
to be a hydrated phosphate of aluminium and calcium. The speci-
mens show its occurrence on quartz, with copper-pyrites in one case,
and with fluor spar in another.

Felspars, etc. (Nos. 795 to 800).

In the fissures or drusy cavities of granitic rocks, the component
minerals — notably the felspar — may occasionally be found in well-
developed crystals. The specimen No. 795, from St. Austell, shows
crystals of opaque white Orthoclase, or potash-felspar, associated
with pale sea-green apatite, and the yellowish-green micaceous
mineral called gilbertite. Minute cubes of pyrite are scattered
sparsely over the felspar.

In the tray numbered 797 are two large, thin tabular crystals of
orthoclase, showing the composite twin forms known as " Carlsbad
twins." Such crystals have the broad planes of the clinopinacoid
well developed, and are said to present the " sanidine habit," since
the variety of orthoclase called sanidine is typically tabular. The
crystals here exhibited come from Caudle Down, St. Austell, and
have suffered partial kaolinisation, so that they present a dead
white appearance, with a rough, dull surface. Some of the por-
phyritic granites of Cornwall exhibit very large crystals of white
orthoclase, with a beautiful zonal structure marked by inclusions,
as may be seen in several of the polished columns and other orna-
mental objects in the Hall. The alteration of felspar with produc-
tion of kaolin, or china-clay, has already been referred to (p. 10).

The polished specimen, No. 798, from the^Triassic conglomerate
of Heavitree, near Exeter, displays the flesh-red crystals of a variety

Nummary of Progress, Oeol. Surv. for 1!)01 (1902), p. 42.
t Journ. Ohern. Hoc. [2], vol. iii. (180'5), p. 2(j:j.

lOO JIINJRALS OF CORNWALL AjnU UKVON

of orthoclase, which was named by Levy, in 1827, after Sir Roderick
I. Murchison (b. 1792, d. 1871).* Murchisonite is notable for the
peculiar sheen, or schiller, which it exhibits on one of its cleavage-
planes.' r . The mineral may possibly be an altered felspar from the
granite'of Dartmoor.

Crystals of Albite, or soda felspar (No. 799) are sometimes found
studding the walls of fissures in the Devonian slaty rocks of North
Cornwall. Excellent crystals occur, in association with quartz
and calcite, in the joints of the slates at Tintagel. The minerals
of this locality have beenVell described by Mr. H. L. Bowman. - ) -

On the albite of Lanterdan Quarry, Prof. Miers discovered Mona-
zite J — a phosphate of the rare cerium metals, which in recent years
has been used in the preparation of mantles for incandescent gas-
lights. Monazite is usually associated with titanium minerals,
and it is therefore not surprising to find that needles of rutile are
found with it on the Tintagel albite, whilst anatase occurs in the
immediate neighbourhood.

In the tray No. 800 are two specimens of Pinite in a schorlaceous
elvan from St. Hilary, in West Cornwall. Pinite is a mineral not
infrequent in the granites and elvans of the Land's End district ;
and here, as elsewhere, it seems to be an alteration-product of
cordierite.§ The cordierite is a silicate of aluminium and mag-
nesium, with more or less iron, which readily suffers transformation
into micaceous and other substances. In pinite, which is some-
times regarded as an impure massive variety of muscovite,' the
form of the original cordierite is faithfully retained, so that the
mineral seen in these specimens may be regarded as a true pseudo-
morph. Mr. J. H. Collins has suggested that the Cornish pinite
may in some cases be pseudomorphous after nepheline.H

Garnets, etc. (Nos. 801 to 808).

Garnet is hardly to be regarded as an uncommon mineral in
Cornwall, though good crystals are not of frequent occurrence.
Some of the best occur in the cliffs in the neighbourhood of Botal-
lack, in West Cornwall, whence the examples here shown as Nos. 801
to 802 have been obtained. These rather resemble the iron-alumina
garnets known as almandine. They present a deep red 'colour —
so deep as to'appear almost black in the stout crystals, but showing
colour and translucency towards the edges. In form they are well-
developed icositetrahedra — or solids bounded by twenty-four

* " On a New Mineral Substance proposed to be called Murchisonite."
Phil. Mag., vol. i. (1827), p. 448.

f " On Monazite aDd Associated Minerals from Tintagel, Cornwall," Min.
Mag., vol. xii. (1900), p. 358.

% " On Monazite from Cornwall," Min. Mag., vol. vi., 1886, p. 64.

§ For the nature and formation of th'S mineral the following paper should
bn consulted : " Tho Natural History of Cordierite and its Associates." By
J. J. H. Teall, M.A., P.R.S., Proc. Oeol. Assoc, vol. xvl, 1900, p. 61.

|| " On tin; Pinite of Breage in Cornwall," Min. Mag., vol. x. (1894), p. 8.

GARflCT t'HLUKIH.. ETC. 101

trapeziums. These crystals are embedded in a dark amphibolite,
or hornblende-schist, from which they are readily detached, leaving
very sharp impressions in the matrix.

Common garnet is now generally known as andradite, including
the varieties sometimes regarded as allochroite and colophonite.
Xo. 805, from St. Just, shows garnet of orange-brown colour, crys-
tallised not very distinctly in rhombic dodecahedra, having the edges
truncated by planes of the icositetrahedron, and associated with
asdnite. Somewhat similar garnet from Okehampton, in Devon,
is seen in No. 803.

In the specimen No. 804, from the old Belston Mine, near Oke-
hampton, garnet is associated not only with axinite but also with
copper-pyrites and mispickel. This unusual association, which was
described by Sir W. W. Smyth, occurred in the metamorphic zone
at the margin of the Dartmoor granite, where considerable workings
for copper-ore were at one time carried on.* A similar specimen
is in Case II., No. 159. The minerals were probably developed by
contact-metamorphism.

Among the changes which garnet undergoes that of conversion
into chlorite is not uncommon. This is illustrated by the specimen
No. 802. Here the crystals, while retaining their form, have become
coated with a dull green chloritic mineral. The change generally
occurs along microscopic cracks, the neighbouring garnet becoming
less hard and dense, and gradually assuming a dull green appear-
ance. Some fine pseudomorphs of chlorite after garnet are shown
in the Wall Case 34, but these are not British specimens. f

Chlorite is a general name applied to a number of minerals, more or
less scaly in structure and greenish in colour. They form a rather
ill-defined group, consisting of silicates of aluminium and magnesium,
with iron, etc., and since they contain a large proportion of water
they are sometimes termed hydromicas. The chlorites are usually
alteration-products of felspars, garnet, mica, augite, hornblende,
and other ferro-magnesian silicates ; but in certain cases chlorite may
be an original mineral. By the Cornish miner chlorite is commonly
called peach, and hence a chloritic lode is said to be " peachy."
Whilst the green peach is undoubtedly of this character, it seems that
blue peach is usually a form of tourmaline.

The specimen No. 807 represents Cornish Actinolite, showing the
radiating fibres of green colour and silky lustre characteristic of
this form of amphibole.

No. 808 is a representative specimen of the mineral known as
PrehnUe. This is a hydrated silicate of aluminium and calcium,

* " On the Occurrence of Metallic Ores with Garnet Rock," Journ. B.
Geol. 8oc., Corn., vol. ix. (1878), p. 38. See also Solly in Min. Mag., vol. vi.
(1886). For ore-deposits formed by contact metamorphism, consult a valuable
paper by W. Lindgren, " The Character and Genesis of certain Contact
Deposits," Trans. Am. Inst. Min. Ewj., voL xxxi. (1902), p. 220

(• On the alteration of garnet into chlorite see Am. Journ. He. [3], vol. x.
(1875), p. 17, and vol. xxxii (1886), p. 307.

102 MINERALS OF CORNWALL

occurring in the cliffs near Botallack and at some other localities in
St. Just. It will be subsequently noticed in connection with the
fine specimens from Scotland (p. 216).

Serpentine, etc. (Nos. 809 to 817).

Among the various hydrous silicates shown in this case bhe most
interesting is the mineral substance well known as Serpentine. This
occurs, however, as a rock rather than as a definite mineral
species. Several specimens of the beautiful rock from the Lizard
district are placed here, under the numbers 809 to 813, and others
are exhibited in Section IV. of the Horse-Shoe case ; whilst a number
of objects in the Hall of the Museum show the material worked as
an ornamental stone in the form of columns, vases, etc. The origin
of the Lizard serpentine has been specially studied by Prof. Bonney,
who showed many years ago that it had been formed from the
alteration of intrusive igneous rocks.*

Serpentine usually results from the metamorphism of rocks rich
in olivine, like the peridotites. Olivine, which is a silicate of mag-
nesium, with more or less iron, is a mineral very prone to alteration.
Its conversion into serpentine, a hydrous silicate of magnesium, can
be traced as it proceeds along the cleavage cracks and curved fissures
of the crystals. Pseudomorphs of serpentine after olivine are well
known. Opaque granules of magnetite are usually present, and
represent the iron eliminated from the olivine during serpentinisation ;
or the iron, passing wholly into the ferric state, may make its appear-
ance as haematite or as limonite. The conversion into serpentine
is accompanied by considerable increase of volume (above 30 per
cent.), and probably involves reactions more complicated than
simple hydration.

It was shown many years ago by the brothers Rogers that silicate
of magnesium may be decomposed by carbonated waters.f This
conclusion was confirmed by the experiments of Mr. A. Johnstone,
of Edinburgh, who observed that water charged with carbonic acid
attacks olivine. j Magnesium carbonate, or Magnesite, occurs in
white veins and patches in the Lizard serpentine. The production
of magnesite from serpentine evidently involves dehydration.

Mr. Howard Fox called attention some years ago to a substance
curiously like flint, occurring as veins in the serpentine of Kynance
Cove, and an analysis by Mr. Hort Player showed it to be the mineral
called pseudophite.% This mineral may, perhaps, be placed in the
chlorite group (No. 815).

* See especially his papers in Quart. Journ. Geol. Soc, vol. xxxiii. (1877),
p. 884; and vol. xxxiv. (1878), p. 769; Geol. Mag. n.s. [2], vol. vi. (1879),
p. 362 ; and [3] vol. i. (1884), p. 406. See also Gen. M'Mahon's address " On
the Manufacture of Serpentine in Nature's Laboratory," Proc. Geol. Assoc,
vol. xi. (1890), p. 427. Also: " British Petrography." By J. J. H. Teall,
1888, p. 104.

t Amer. Journ. Soc. [2], vol. v. (1848), p. 401.

% " On the action of carbonic acid water on olivine." Proc. Roy. Soc. Edin.,
1888.

§ Min. Mag., vol. ix. (1892), p. 275.

ALLOPHAXK. ETC, 103

Steatite, or soapstotic (No. 816) occurs in the Lizard serpentine,
and was at one time worked as a material for the manufacture of
porcelain, as also as a source of various magnesian salts. It is a
hydrous magnesium silicate, and may be regarded as a massive
variety of talc. Saponite (No. 817) is a somewhat similar mineral,
but contains much aluminium silicate.

With the Cornish serpentine is placed a specimen of Diallage
(Xu. 814) from the gabbro of Crousa Downs, not far from the Lizard.*
The rock called gabbro is a crystalline aggregate of diallage and
plagioclase felspar, with oUvine. The dead-white mineral in the
coarse gabbro is saussurite, an alteration-product of the plagioclase,
whilst the diallage, which is a variety of augite, is distinguished by
the bronzy lustre displayed by what appear to be its cleavage planes.
These represent directions of chemical weakness along which the
mineral has suffered that kind of alteration which Professor Judd
has distinguished as schillerisation.'f Microscopic lamellar enclos-
ures have been developed along these planes of parting, and to these
secondary minerals the metalloid lustre, or schilhr, of the diallage
is due.

Allophane, etc. (Nos. 818 to 824).

Several amorphous silicates of aluminium are here grouped to-
gether. The specimens 819 and 820, which attract the eye by their
delicate blue colour and pearly lustre, are examples of the hydrated
aluminium silicate termed Allophane. In these specimens the mineral
recurs in small botryoidal masses, on black carbonaceous shale,
from Wheal Hamblyn, near Bridestone, in Devonshire. The blue
colour is due to admixture with some copper mineral, probably
chrysocolla, as the cupreous allophane is said to pass in some cases
into this copper silicate. The opaline allophane, like these speci-
mens, has been distinguished as Schrutterite.

In No. 818 the allophane is tinted green, presumably by malachite,
and is partially encrusted with brown hydrated oxide of iron,
associated with a little native copper, in delicate sprigs, coated with
the green carbonate. Allophane seems always to be a secondary
mineral derived from various aluminous silicates, especially felspars.
It is not infrequent in certain copper mines.

The massive opaque substance generally called Lithomarge is re-
presented by Nos. 821 and 822. Some of the Cornish " lithomage "
may be referred to the species halloysite. In No. 822, from Tucking-
mill, near Camborne, the white substance is marked with irregular
stripes of purple colour. No. 823 represents the mineral from
Restormel, which Prof. Church has distinguished as Restormelite.\

* For description of the Crousa Down gabbro see " British Petrography,"
by J. J. H. Teall, M.A., p. 174.

t On schillerisation see Prof. Judd's papers in Quart. Jonrn. Oeol. Sue-,
vol. xli. (1885), p. 383 ; and M in. Mag., vol. vii. (1887), p. 81.

% Journ. C'hem- Soc, Vol. xxiiL, (1870), p. 1<J5.

10-1 MINERALS OE CORNWALL AND DEVON.

The earthy substance, of dull green colour, numbered 824, is a
sample of Chloropal from Haytor in Devonshire. This is a hydrated
silicate of iron.

Pigotite (No. 825).

Under the name o.f Pigotite, Prof. Johnston, of Durham, described
in 1840 a Cornish mineral which he regarded as a compound of
alumina with an organic acid termed by him mudesous acid.* To
this body, in its anhydrous condition, he assigned the formula
C 12 H 6 8 . It was assumed that the acid had resulted from the decay
of superficial vegetation on the moorland,f and having been carried
down to a mass of decomposing granite had attacked the felspar.
The product was found as an incrustation on the walls of certain
caves in granitic cliffs in Cornwall. The specimens here exhibited
from St. Levan, which have recently been presented by J. W.
Wetherell, Esq., rather resemble a dark brown wood-opal.J The
name was given to the mineral in compliment to the Rev. M. Pigot,
who, with Prof. Johnston, first observed it.

Retinite (No. 826).

Associated with the Tertiary lignite of Bovey Tracey, in Devon-
shire, there are occasionally found small irregular masses of a brown
resinous substance, usually earthy in appearance, such as the speci-
men No. 826. This substance was examined by Hatchett, who
named it RetinasphaU, since he regarded it as partly resinous and
partly bituminous.§ Subsequently it was analysed by Prof. J. F. W.
Johnston of Durham.ll It is now usually designated Retinite, and
appears to be a fossil resin exuded from the coniferous trees which
contributed to the formation of the Bovey coal. The characteristic
conifer is the Sequoia couttsice of Heer, a tree allied to the mammoth
tree of California.^ It may be noted that the term ' retinite ' is
now used as a rather general name for a number of fossil resins more
or less akin to amber, but usually occurring in lignite.

Various mineral hydrocarbons, including petroleum, have occa-
sionally been found in some of the mines of Cornwall and Devon, and
carbon in the form of Graphite is not unknown, as witnessed by
specimens in the Horse-shoe Case Section A.

The collection of British Minerals is continued in Case VII., on
the opposite, or eastern, side of the Museum.

* " On the constitution of Pigotite, and on the Mudesous and Mudesic
Acids." Phil. Mag., vol. xvii. (1840), p. 382.

■f Hence the name, from fivStiatg (mudesis), decay.

t " On the occurrence of Pigotite in the caves near Porthcurnow, St. Levan,
Cornwall." By J. K. Creighton, Oeolog. Mag. n.s. [iv.], vol. i. (1894), p. 223.

§ Phil. Mag. vol. xxi. (1805), p. 147.

|| " On the Composition of Certain Mineral Substances of Organic OrigiD."
Part iv., " RetiDasphalt." Phil. Mag., vol. xii. (1838), p. 560.

H Phil. Trans., vol. 152 (1863), p. 1051.

uTSHIRE. 10")

CASE vn.

DIVISION 1.
MINERALS OF SOMERSETSHIRE, WALES, ETC.

MINERALS OF WEST SOMERSET.

{Nos. 827 to 8?.2).

The minerals of Cornwall and Devon, which have been described
in the preceding pages, occupy six out of the twelve table-cases
in which the Collection of British Minerals is installed. Justifica-
tion for this disproportionate allocation of space may be found in
the fact, previously stated, that these counties far surpass any other
mining district of Britain in the number, the variety, and the beauty
of their minerals. Moreover, the Ludlam Collection, as before re-
marked, is particularly rich in fine specimens from the mines of the
two south-western counties.

Following the minerals of Cornwall and Devon, those of West
Somerset may be conveniently considered. A few specimens of
Malachite and Azurite exhibited in this case (Xos. 827 to 829) serve
to recall the old attempts at copper-mining in the Triassic rocks
on the north-east of the Quantocks. The principal workings were
situated between Doddington and Nether Stowey. According to
Mr. Leonard Horner,* the Doddington copper mine had but a brief
existence, the cost of pumping being greater than the value of the
ore that was raised. The ore was principally a mixture of the green
and blue carbonates, resulting from the alteration of copper-pyrites.

Of these two basic cupric carbonates, it is notable that the azurite,
or blue ore, often occurs in crystals, whilst the associated malachite,
or green ore, may be merely mammillary in form or fibrous in texture.
The blue carbonate is a mineral of more limited occurrence than
the green carbonate, into which it seems rather readily to pass.

By far the most important minerals in West Somerset are the
Iron-ores of the Brendon Hills. These hills range in an east-and-
west direction, about six miles south of the coast between Minehead
and Watchet. They consist of rocks like much of the Cornish
lrillas, and have been worked for slates at Treborough. In these
slaty rocks, the iron-ore occurs in veins, which, according to the
late Mr. Etheridge, occupy fault-fissures. The body of ore consists
of C'halybite, or Siderite, occurring in cleavable crystalline masses,

* " Sketch of the Geology of the South-western Part of Somersetshire."
By Leonard Horner, Esq., F.R.S. Trans. Ged. Soc., vol. iii. (1816), p. 383.
7882 I

10(i MINERALS OF SOMERSE

A.I3n.J.T\Ii.

known as spatliose, sparry or spathic iron ore ; but this ferrous car-
bonate, being readily altered by superficial agencies, becomes con-
verted in the upper part of the veins into brown and red oxides of
iron. With these oxides the unaltered ore offers so strong a contrast
by its pale fawn colour that it is known as " white ore.'" The Brendon
iron-ores are represented by Nos. 831 to 832.

Like that of many other localities, the spathic ore of the Brendon
Hills contains manganese — presumably in the form of carbonate,
since manganous and ferrous carbonates are isomorphous. Ac-
cording to an analysis by Mr. J. Spiller, the ore contains as much
as 12-64 per cent, of MnO.* By superficial alteration, the mangan-
ese takes the form of hydroxide, so that the brown iron-ore at the
outcrop is associated with much oxide of manganese. In conse-
quence of the high proportion of manganese in the Brendon ore, it was
peculiarly fitted for the manufacture of spiegeleisen, and at one time
was largely worked for this purpose by the Ebbw Vale Company,
and exported to South Wales. Relics of old workings show that
the ore was wrought at a very early period, perhaps by the Romans.
The mines and the ore have been described by Mr. Morgan Morgans,!
who was in charge of the workings thirty years ago, and to whom
the Museum is indebted for the interesting specimens in the tray
No. 832, showing pseudomorphs of haematite after rhombohedra
of chalybite.

Spathose ore, similar to that worked at the Gupworthy mine and
elsewhere in the Brendon Hills, occurs under similar conditions,
in the slaty rocks of Exmoor — a range extending from West Somer-
set into North Devon. According to the late Sir W. W. Smyth,
the Exmoor veins course about E. 10° S.J The ferric hydroxide,,
resulting from the alteration of the spathose ore, occasionally
takes the form of gothite, crystals of which line the cavities in the
ore. No. 830 is a specimen of the Exmoor chalybite.

At Wheal Eliza, on Exmoor, the iron-ore was associated w r ith dis-
seminated copper-pyrites, and the vein was at one time worked
for copper. Spathose ore is not infrequently accompanied by ores
of copper and lead, notably by argentiferous galena — an occurrence
illustrated at Weardale in Durham, where the ore occurs in Car-
boniferous Limestone.

In limestone districts, spathose ore may sometimes have been
formed by the reaction of the carbonate of lime on ferrous sulphate
from decomposed pyrites. But the ore of the Brendon Hills and
Exmoor is not directly associated with limestone, though irregular

* " Metallurgy." By John Percy, M.D., F.R.S. Vol. " Iroc and Steel,'!
1864, pp. 210, 227.

f " The Brendon Hills Spathose Iron Ore and Mines." By Mr. Morgan
Morgans. Trans. South Wales Inst, of Engineers, vol. vi. (1870), p. 79. Also
" On a Peculiarity of the Brendon Hills Spathose Iron Ore Veins." Quart.
Journ. Geol. Soc, vol. xxv. (1869), p. 255. The peculiarity in question is the
" end- slant " of the pockets of ore.

J " On the Iron -ores of Exmoor." By Warington W. Smyth, Esq., F.R.S
Quart. Journ. Geol, Soc, vol. xv. (18.59), p. 105,

MENDIP MINERALS. 107

calcareous bands are not far off. Its occurrence rather recalls that
of the spathose ore in the Duchy Peru lode in Cornwall, or more
closely that of the fine deposits in the Devonian slaty rocks at
Siegen in Westphalia. The carbonate of iron seems to have resulted
not from a process of substitution, but rather from direct precipita-
tion on the walls of the vein. The ore is accompanied by quartz.
Possibly certain iron silicates in the rocks may have been decom-
posed by carbonic acid in the underground waters, with formation
of ferrous carbonate and reparation of silica.

At the present time no iron ore is raised either from the Brendon
Hills or from Exmoor.

Minerals of the Mendips.
(\os. 833 to 845).

Whilst the Mendip Hills have gi\ en their name to a rare mineral,
Mendipite, it is said, on the other hand, that thev received their
name from their mineral wealth, the modern term Mendips being a
corruption of the old term ' : .Myne Deeps." The principal minerals
are the ores of lead and zinc, though minerals containing copper and
manganese are not unknown, whilst iron-ore is in some places rather
abundant.

The Mendip plateau is a stretch of high ground in Somersetshire,
extending from near Frome in a north-westerly direction as far as
the Bristol Channel, a little south of Weston-super-Mare . It thus
forms a broad belt of table land, about thirty miles long, though not
more than five miles in width, running in a N.W. and S.E. direction,
and reaching a maximum height of 1,060 feet. Its geological
structure has been described by Mr. H. B. Woodward, F.R.S.*

The Mendip range consists of Carboniferous strata, resting conform-
ably on Old Red Sandstone. These strata have been thrown into a
succession of anticlines, having their axes striking E. and W., and
the summits of the folds have suffered denudation, so that the Old
Red Sandstone, forming the nucleus of the range, is here and there
exposed. Patches of Dolomitic Conglomerate — an old beach deposit
of Triassic age — rest unconformably on the upturned and denuded
edges of the Carboniferous strata. Much of this conglomerate has
no doubt been removed by denudation ; yet fragments still lie on the
flanks of the hills and in some places cap the high ground. It is this
Dolomitic Conglomerate and the Carboniferous Limestone which
form the principal repositories of the minerals of the Mendips.

Lead-Ores (Nos. 835 to 837).

So far as the lead-ore is concerned, it is certain that it engaged the
attention of the Romans, and probably it had not been overlooked
even in pre-Roman days. Pigs of lead bearing Roman inscriptions,

* " Geology of East Somerset and the Bristol Coal-fields." Mem. Gcolog.
Survey, 1876. Also : Proc. Geol. Assoc, vol. xi. (1891), p. 481. The Survey
Memoir contains a " List of Minerals found in the Area." p. 176.

7HS-2- I -1

108 MINERALS OF THE MENDli'8.

with ruins of smelting houses rich in relics of Roman occupation, in
the shape of pottery and coins, have been discovered at Charter-
house, between Priddy and Blagdon.* So extensive were the early
smelting operations that in recent years the old waste heaps of slag,
and even the slimes and tailings, have been re-worked. This refuse
matter has been found to contain on an average about 12 per cent, of
metallic lead. It consists of materials belonging to various periods of
working, but it is not unlikely that in some cases the modern work-
man is re-handling the very refuse of the Roman smelter.

In this refuse, as in the old Roman lead-slags of Laurion, in Greece,
various secondary minerals have been developed ; and among these,
Mr. L. J. Spencer, of the British Museum, has detected the rare
mineral Leadhillite.^ This was found in cavities of slag, which
occurred in association with fragments of charcoal and masses of
galena, only partially fused. Some of the lead had been converted
into carbonate, sulphate and sulphato-carbonate, which had crystal-
lised in the free spaces, and thus afforded an interesting illustration
of the recent formation of the oxidised lead -minerals known
respectively as cerussite, anglesite and leadhillite.

The primitive lead ore of the Mendips, as elsewhere, is Galena
(Nos. 835, 836). According to Mr. T. Morgans,! the lead-ore occurs
chiefly in the form of lumps of galena, associated with the oxides of
manganese and iron, in veins of clay, filling fissures which seem to
run mostly along joint-planes. Strings and nests of galena occur
both in the Carboniferous Limestone and in the Dolomitic Conglom-
erate, often associated with more or less cerussite, or lead carbonate,
and with a matrix principally of calcite. As the " old men " or
" groovers," as the miners of bygone days are called, were prevented
from deep working by the trouble of water, they were confined to
limits, rarely, if ever, exceeding, and but rarely reaching, a depth
of thirty fathoms.

Mendipite (Nos. 839, 840).

The two specimens, Nos. 839 and 840, are examples of the rare
mineral called Mendipite. It appears that an old specimen labelled
" Lead spar from Mendip " was examined by Berzelius in 1823, and
determined to be an oxychloride of lead ; and to this species
Glocker in 1839 gave the name by which it has ever since been known.
The specimens exhibited are from Churchill, the original locality,
and show the mineral associated with oxide of manganese.§ It will
be seen that the mendipite forms crystalline cleavable masses, of

* See Prebendary Scarth : Journ. Archosolog. Assoc, vol. xxi. (1875),
p. 129.

■f " Leadhillite in Ancient Lead Slags from the Mendip Hills." Rep. Brit.
Assoc, for 1898, p. 875.

J " Notes on the Lead Industry of the Mendip Hills." Trans. Inst.
Mining Eng-, vol. xx. (1902), p. 478.

§ From this locality the mineral has sometimes been called C'hurchittite
but the name is now obsolete.

MendifiTe, etc. 1<j9

columnar structure, yellowish white in colour and slightly adaman-
tine in lustre. The mineral belongs to the orthorhombic system,
but distinct crystals are unknown.

Mendipite was discovered some years ago near Priddy, in the
workings of the Somerset Manganese and Iron Company.* It
there occurs in the Dolomitic Conglomerate, associated with a
little copper-ore and oxide of manganese.

The oxychloride of lead is no doubt a secondary mineral, derived
directly or indirectly from the alteration of galena. At Churchill it
occurred with galena, and at Priddy with cerussite. The occurrence
of an oxychloride suggests that waters containing chlorides have been
active in the oxidation-zone of the mineral-deposit. Possibly
Triassic rocks, more or less saliferous, once spread over this area.
But, apart from such strata, the analysis of ordinary sedimentary
rocks frequently reveals the presence of chlorides, and moreover, in
inland fresh waters, chlorides are sufficiently common. According
to Prof. E. Kinch the annual average amount of common salt in the
rain-water falling at Cirencester is as much as 36 lbs. per acre.t

It is not surprising, then, that meteoric waters percolating
through deposits of lead-ore may sometimes give rise to the
formation of chlorides, such as are occasionally found in the shallow
parts of certain ore-bodies, and are represented in the Mendip
area by mendipite.

Zrrtc-<yres (No. 838).

The zinc-ore formerly worked on a large scale in the Mendips was
chiefly in the form of the carbonate called Calamine. Some con-
fusion has, unfortunately, arisen in mineralogical nomenclature with
regard to this word. In England the term " calamine " is com-
monly applied to the carbonate of zinc, whilst elsewhere the word is
frequently used by mineralogists to denote the hydrous silicate,
whilst the carbonate is designated as Smithsonite. By miners, the
term " calamine " is often applied indifferently to both carbonate
and silicate, and it appears that both species were included under the
old name of lapis calaminaris.i The separation was first distinctly
pointed out by James Smithson, who analysed the minerals a
century ago, and apologised for the imperfection of his work on the
ground that " chemistry is yet so new a science."! An example of
the calamine is furnished by No. 838.

It was not until the early part of the eighteenth century that the
value of calamine as an ore came to be recognised. At that time, it

* Proc. Oeolog. Assoc, vol. xi. (1891), p. cxcix. The history of mendipite is
here given by Mr. H. B. Woodward, F.R.S.

t Journ. Chem. Soc, 1900, Part i., p. 1271. This estimate is based on
investigations carried on for the last twenty -six years, and it assumes that all
the chlorine in the rain occurs as sodium chloride. See also recent analyses
by Mr. W. W. Fisher in The Analyst, 1904.

+ See "The Nomenclature of Zinc-ores."- By W. R. Ingalls. Trans. Am
Jnst. Min. Eng., vol. xxv. (1896), p. 17.

§ " A Chemical Analysis of some Calamines." By James Smithson, F.R S.
Phil. Trans., vol. xciii. (1803), p. 12

110 MINERALS OF THE MESTDIra.

came into use not so much for the production of metallic zinc, or
spelter, as for the preparation of yellow metal, or brass. The
calamine was worked chiefly at Eowberrow, Shipham, and Harptree;
and the calcined ore was sent to the brass-houses of Bristol and
Birmingham.

Most of the calamine of the Mendips was found in the Dolomitic
Conglomerate, where it occurred partly as veins and partly dissemi-
nated through the rock, often in small fragments resembling gravel.
It was probably derived from the alteration of sane-blende, the
common ore of zinc. Oxidation of the blende, which is a sulphide
of the metal, produces sulphate of zinc, which, reacting with the
limestone or with the dolomite, might form zinc carbonate. Deposits
of calamine may occur even in deep-seated zones, if within reach of
fissures which have afforded a channel for the descent of surface
waters. M. Lodin's views on the formation of calamine are
referred to at p. 142.

Although zinc-blende seems to be a very rare mineral in the
Mendips, it probably exists at considerable depth as the primary
ore of zinc. It rarely happens that ore-deposits which contain
galena are destitute of blende, but it is common for the blende to
occupy a deeper zone. Galena is a rather stable sulphide, whilst
blende is more readily attacked by meteoric agencies, and easily
converted into oxidised compounds like the sulphate and carbonate.

Calamine is a common and characteristic mineral in dolomite.
Dieulafait showed that it might be assumed, on thermo-chemical
principles, that the formation of calamine from zinc sulphate was
more likely to occur by reaction with magnesium carbonate than
with calcium carbonate.* It is notable that generally the occurrence
of ores, both of lead and zinc, seems to be more common in limestones
which are magnesian than in those of normal type. The dolomitic
rock lends itself readily to metasomatic replacement! ; and as Mr.
H. F. Bain has pointed out, the porous, or even cavernous, texture
of magnesian limestone must favour the circulation of underground
waters, and so promote chemical changes.*

Calamine does occur, however, in the Carboniferous Limestone
of the Mendip area ; and pseudomorphs are known in which zinc
carbonate has taken the form of fine scalenohedra of calcite, such
as might occur in fissures of the limestone. s

Iron-arts (Xos. 833, 834).
Iron-ores are of very common occurrence in the Dolomitic Con-
glomerate. The brown and red oxides are to be found, as Mr.
Ethevidge remarked, wherever the conglomerate rests on the Car-
boniferous Limestone, on the Millstone Grit, or on the Pennant Grit.

* Compter Rendns. vol. ci. (1SS5), p. 842.

t Mrtitoma/ism is a term used to express a change of substance in a
mineral body, effected usually by hydro -chemical action. It differs from
rs'-ndomorphism since it does not necessarily connote retention of form

+ U. S. Geo!. Surv., '22nd. Ann. Rep., Partii., 1901, p. 209.

§ Voi- further remarks on Calamine see pp. 141, 166.

POTATO-STONES. Ill

It occurs not only in the conglomerate itself, but also in faults,
fissures, and pockets in the underlying Carboniferous rocks. It
has been suggested that the iron oxides of these Carboniferous de-
posits have been derived in many cases from red rocks, Triassic
or Permian, by which they have at some time been overlain. The
specimen No. 834 represents the iron-ores of the Mendips.

It was from the Dolomitic Conglomerate, resting on Carboniferous
Limestone and Millstone Grit, that the red ochre called reddle or
ruddle was at one time extensively extracted at Heath Hill, south
of Winford, on the north of the Mendip area. Pits reaching in some
cases to more than fifty feet in depth, were sunk * The reddle
was an argillaceous ferric oxide, forming a deposit which reached
as much as six feet in thickness. The mineral has also been exten-
sively worked in recent years.

Potato-stones (Nos. -S42 to 846).

Among the minerals of the Dolomitic Conglomerate mention
should be made of the curious siliceous nodules known as Potato-
stones. A small series of these nodules is here exhibited (Nos. 842
to 845). They are rather widely distributed, occurring south and
east of the Mendips, near Wells and Cheddar, and on the north
at Clevedon, and also at several localities near Bristol.

The potato-stones present usually a crust of chalcedonic silica,
rough on the outside, and lined internally with crystals of quartz.
Other minerals, such as calcite and celestite, are also found sub-
ordinately inside the geodes. Prof. Rupert Jones, from the study
of a large collection in the Museum of the Geological Society, was
led many years ago to suggest that the nodules had their origin
in the replacement of limestone by silica.} This suggestion seems
highly probable.

In the Dolomitic Conglomerate there are numerous fragments
and pebbles of Carboniferous Limestone, united by a cement which
is more or less magnesio-calcareous or dolomitic. Such pebbles
might readily undergo metasomatic alteration, whereby the carbon-
ate of lime was gradually removed and silica deposited in its place,
with more or less retention of external form. The molecular substi-
tution of silica for calcium carbonate is a change which has come
to be widely recognised by chemical geologists. The process of
replacement, starting from the exterior of the nodules, was usually
not continued far enough to form a solid siliceous mass. Water,
gaining access to the interior of the mass, might remove the central
calcareous part, leaving a hollow in which siliceous solutions slowly
deposited crystalline quartz as a lining of the geode. In some cases
chalcedonic layers alternated with deposits of a distinctly crystalline
character, and a true agate, with a regular succession of zones,

* Trans. Oeolog. Soc., 2nd series, vol. i. (1824), [j. 308.

t " Od Quartz, Chalcedony, Agate, Flint, Chert, Jasper, and Other Forms
of Silica Geologically Considered." By Prof. T. Rupert Jones, F.R.S. Proc.
Oeolog. Assoc, vol. iv. (1876), p. 439.

112 MINERALS Oi? BRISTOL.

was produced. Probably the chemical activities of the circulating
waters were accelerated by heat; and the siliceous solutions saturat-
ing the rock, perhaps buried at a considerable depth, deposited
crystalline minerals in all accessible situations, so that the cavities
between the fragments of the breccia are in some cases lined with
crystals.

Some of the potato-stones exhibited here, and in a table-case
on the opposite side of the room, were presented by Spencer G.
Perceval, Esq., of Henbury, and others by the late Swinfen
Jordan, Esq. Several of them display beautiful agates in their
interior.

Minerals of the Bristol District.
(Nos. 847 to 858).

Many of the minerals already noticed as occurring in the Mendips,
re-appear under similar geological conditions in the neighbourhood
of Bristol. At the same time each district has certain minerals
peculiar to itself. A list of the minerals occurring in the neighbour-
hood of Bristol, prepared by Mr. E. Wethered, has been published
by the Cotteswold Club.*

Galena and copper-ores occur in small quantity in the Dolomitic
Conglomerate ; manganese is rather widely distributed ; and iron-
ores, in the form of haematite and limonite, occur in such abundance
as to be occasionally worked commercially.

Iron-ores, etc. (Nos. 847 to 854).

Rather more than thirty years ago an iron-mine was opened
in the Royal York Crescent at Clifton, and was described by Mr.
J. G. Grenfell. It was sunk in the Millstone Grit, which is overlain
by Triassic strata rich in iron. The principal ore was limonite,
but this was associated with haematite, often found in the interior
of the lumps of ore, and with gothite, occurring sparingly in crystals.^

Some of the specimens here exhibited show the limonite in staiac-
titic forms (Nos. 847, 850) ; and from the vertical position of the
stalactites in the cavities of the ore it seems, as Mr. Grenfell pointed
out, that their formation must have been subsequent to the move-
ments which tilted the enclosing rocks.

At Iron Acton, Frampton Cottrell, and some other localities
north of Bristol, which have yielded much heematitic iron ore, the
mineral occurs in the Pennant Grit, which is referable to the Middle
series of Coal Measures. The ore has no doubt been introduced,
as Mr. Etheridge suggested, from the iron-bearing Triassic or other
red rocks which overlie, or at some time have overlain, these strata.J

* Proc. Cotteswold Club, vol. viii. (1886), p. 30.

•j- Trans. Clifton Coll. Sci. £oc.,Partiv., p. 46; Oeol.Mag. (n. s.) vol. i. (1874)
p. 179.

% Quart. Journ. Oeol. Soc, vol. xxvi. (1870), p. 183. Proc. Cotteswold Nat
Club, vol. iv. (1868), p. 47.

CKLESTITE. 113

From the upper beds the iron may have migrated downwards, by
means of descending solutions, and the impregnation of the Car-
boniferous rocks and the infilling of their cavities with iron oxides
may be a process which, as Mr. H. B. Woodward remarks, is in
some cases even still in progress.*

On some of the specimens of Bristol iron-ore here exhibited, such
as No. 852, the limonite carries beautifully defined crystals
of quartz. It will be noted that some of the crystals are doubly
terminated ; that is to say, the six-sided prism is attached by one
of its lateral faces to the matrix, whilst each of the free ends is capped
by a six-faced pyramid. The brilliant crystals of quartz in several
of the specimens (Nos. 851, 854) display a red colour, more or less
pronounced, due to enclosed oxide of iron, and recalling the speci-
mens of Eisenkiesel from the Restormel Royal Iron Mine in Cornwall
(p. 92). Many of the crystals of red quartz have been derived
from the interior of the potato-stones found near Bristol. The
small but well-defined crystals in the tray No. 846 have been ob-
tained from such a source ; some of them are bi-pyramids of quartz,
whilst others are scalenohedra of calcite. The quartz crystals,
when colourless and pellucid, are sometimes known as Bristol Dia-
monds, or Bristol Stone. In No. 841, crystals of calcite, tinted pink
with oxide of iron, are seen studding the walls of a geode ; and
occasionally celestite may be found in a similar position.

Celestite (Ms. 855 to 858).

To the student of mineralogy the Celestite or celestinef, a native
sulphate of strontium, is the most interesting of all the minerals
occurring in the neighbourhood of Bristol. Several representative
specimens are here shown (Nos. 855 to 857), but with these the
visitor should compare the suite of specimens in the Central Horse-
shoe Case (Section G), which includes some examples of this mineral
exceptional for size and beauty.

The celestite of Bristol occurs in the lower beds of the Keuper
marls. At Clifton and Durdham Downs it has been found in the
Carboniferous Limestone, not however in the rock itself, but simply
in fissures to which it has probably gained access from overlying
Triassic strata. Mr. H. B. Woodward cites a number of localities
which yield celestite in the district of Bristol and East Somerset-
shire.! including some in the Oolites and the Rhaetic beds.

Some of the finest crystallised specimens were obtained from
Pyle Hill, when the Bristol and Exeter Railway was in course of
construction. Other specimens, of remarkable size and perfection

* Mem. Oeol. Surv., E. Somersetshire and Bristol Coal-fields, 1876, p. 166.

■f Celestine is the usual form of the word, but Dana many years aeio
advocated the general use of the termination -ite in mineral names. The
ending in -ine is chemical rather than mineralogical.

t Op. cit., p. 176. See also : " Observations on Celestite." By Frederick
Smithe. Proc. Cotteswold Club, vol. x., (1892), p. 71. " Celestine Deposits of
the Bristol District.". By B. A. Baker. Proc. Brist. Nat. Soc., vol. be (1902),
p. 161

] 14 MINERALS OF BRKr;

of form, have been found at Wickwar and at Yate, in Gloucester-
shire, where large deposits were discovered some years ago. The
collection contains representative specimens from all these localities,
those from Yate having been presented by the late H. G-.
Madan, Esq., who was intimately acquainted with the locality
and with the mineral.

None of the Bristol celestite presents the celestial blue colour,
suggested by the name of the species ; yet a delicate bluish tint
is often visible. This has been referred to the presence of a ferroso-
ferric phosphate, but the late Mr. W. W. Stoddart, who examined
many of the bluish specimens, failed to detect in them any trace
of iron.* The reddish tint of much of the celestite is, however,
due to ferric oxide. Mr. Stoddart made the interesting observation
that many plants growing on the celestite-bearing marls near
Bristol contained strontium, which was readily detected in their
ashes by the spectroscope ; whilst the same species growing in
the neighbourhood, but off the marls, were destitute of this
element.

Although celestite is found in veins, and as irregular masses in
the Keuper marl, some of the finest specimens are obtained from
the interior of geodes. The large crystals, of prismatic habit and
in some cases of tabular form, found in these cavities are often
associated with selenite. Such a companionship seems indeed
to be almost universal in the Bristol area. The association of
celestite and gypsum is illustrated by the specimen No. 1401 in
Case XI. As a matter of fact, most gypsum contains more or less
strontium.

Strontium is an element much more widely diffused than was
formerly suspected, although its concentration in notable quantity
is comparatively rare. M. Dieulafait found it in many mineral
springs and in sea-water, as well as in the hard structures of certain
marine organisms. f According to the analyses of Dr. W. F. Hille-
brand, barium and strontium are widely distributed in rocks, though
the proportion is usually below 0-1 per cent. J The water of the
dropping well at Knaresborough, derived from Permian strata,
contains, according to Mr. B. A. Burrell, 0-322 grains of strontium
per gallon, equivalent to 0-672 of strontium sulphate.§ The sul-
phate is present in the deposit from water pumped up from certain
collieries in Durham, as analysed by Professor Clowes. || In many
of the old well-waters of Bristol strontium occurs, derived no doubt
from the celestite in the marl through which the water has
percolated.

* " On the Occurrence of Celestine in the Keuper Marls, and its Influence
on the Composition of Plants." Min. Mag., vol. i'. (1877), p. 4.

•j- Comples Rendus, vol. lxxxiv. (1877), p. 1303.

j Journ. Chem. Soc, 1896, Abstracts, part ii., p. 191.

§ Proc. Yorkshire Oeol. and Polyt. Soc, new ser., vol. xiii. (1895-1899),
p. 135.

|| Report Brit. Assoc, Newcastle-upon-Tyne, 1890, p. 596.

CELESTITE. 1 1 ■"

It is worth noting that celestite has been found, with calcite,
fluor, and galena, in the vein-deposits of the thermal springs of
Bourbon-l'Archambault, in the Department of the Allier.*

The sulphate of strontium being much more soluble in water than
is the corresponding salt of barium, is more frequently found
in natural waters. Yet as a mineral, barytes is far more common
than celestite. The two species are isomorphous, crystallising
in the orthorhombic system, and often assuming a similar habit.

Probably the origin of the celestite in the West of England is
to be traced to the strontium salts in sea-water or in salt lakes. In
some cases, celestite is believed to owe its formation to the action
of sulphate of iron, from decomposing pyrites, on strontianite,
or the carbonate of strontium ; but strontianite is not recorded
among the minerals of the Bristol area. The connection between
celestite and selenite, already noticed, suggests a common origin
for the two sulphates. Dieulafait found that on the spontaneous
evaporation of sea-water, the strontium was accumulated chiefly
in the gypseous deposit, and not in the sea-salt.

The deposits of celestite in Gloucestershire and Somersetshire
are not without economic importance. According to the official
statistics f the quantity obtained from shallow quarries in these
two counties and shipped from Bristol Docks during the year 1902
amounted to 32,281 tons, of the value of as many pounds sterling.

Large quantities of celestite are employed in Germany in the
preparation of beet-root sugar. For sugar refining, the innocuous
compounds of strontium have superseded those of barium, the barium
salt3 being poisonous. The celestite is converted into strontium
hydrate, which is extensively used in Scheibler's process for separating
the sugar as a strontium saccharate. % Celestite also finds application
as a source of other strontium salts, such as the nitrate, which is
used for giving a crimson light in pyrotechny.

The occurrence of celestite, associated with calcite, in cavities of
the Keuper marl under the summit of Peak Hill, near Sidmouth, in
Devonshire, has been recorded by Mr. Spencer G. Perceval,§ and
specimens of the mineral from this locality, exhibited in the Horse-
shoe Case, may be compared with the mineral from the Somersetshire
and Gloucestershire localities.

Since the sulphates of strontium and barium are isomorphous, it
is not surprising that the two salts should occur in natural union.
■Such a mineral is distinguished as Barytocdestite, or barytocelestine.
In digging the foundation of buildings a few years ago in Oakley
Road, Clifton, a mineral unearthed from the Keuper marl was
detected as barytocelestite by Mr. W. H. Wickes. A specimen

* Comptes Rendus, vol. lxxx. (1875), p. 1297.

t Home Office Report: Mines and Quarries for 1902. Part iii., Output.
Edited by C. Le Neve Foster, D.Sc, F.R.S., p. 275.

| Thorpe's " Dictionary of Applied Chemistry," vol. iii., pp. 003. 623.

§ " On the occurrence of Celestine in New Red Marl, near Sidmouth."
Uin. Mag., vol. iii. (1880), p. 255.

116 MINERALS OF DEAN

J.- \y±Y.EiO 1 t

presented by him, is here shown as No. 858.* An analysis of a
specimen from the railway cutting at Chipping Sodbury has been
made by Dr. Pollard in the laboratory of the Geological Survey .f

Minerals of the Forest of Dean.
(Nos. 859 to 862).

Extensive deposits of iron-ore occur in the upper part of the
Carboniferous Limestone and in the lower part of the Millstone Grit,
which crop out as a narrow zone engirdling the little coal-field of the
Forest of Dean, situated between the Severn and the Wye. The ore
is principally Ldmonite, or brown hydrated oxide, associated with a
little red haematite and with reddle, or ochre, which occurs in a thin
vein at the base of the mine-measures. The ore-bearing limestone is
known locally as crease, or crease stone. In this rock the ore occurs
in the form of irregular pockets, connected by strings or leads, and
the removal of the ore leaves caverns, frequently of vast dimensions,
called chums. These irregular spaces, with their limestone buttresses,
often have calcareous stalactites pendant from the roof or bedecking
the walls, and present many of the picturesque features of limestone
caverns. No. 862 is a specimen of calcite crystallised around a
stalactitic deposit from one of these churns.

It has often been suggested that the limestone was originally
cavernous, and that the ore was deposited in such pre-existing
spaces ; but it seems more probable that the removal of the limestone
and the deposition of the ore were concurrent processes, or rather
perhaps that the iron oxide has taken the place of the calcium
carbonate by molecular replacement. This metasomatic action
will be again referred to, in connection with the haematite deposits
of the North of England.

Three kinds of brown iron-ore are recognised in the Forest of Deanj:,
namely: (1) Brush-ore, or limonite in stalactitic, reniform, or compact
masses, sometimes fibrous and radiate in structure, and occasionally
coated with minute crystals of ferric hydrate, so black and brilliant
as to impart a velvety appearance to the surface. (2) Smith-ore, an
incoherent form of limonite, often in a finely powdered condition,
and less rich in iron than the brush-ore.§ (3) Clod, a highly ferrugi-
nous marl, useful as a flux in smelting the ore.

No. 859 is an example of brush-ore, No. 860 of smith-ore, and
No. 861 of grey ore, an ore in which the limonite is associated
with chalybite.

* Proc. Oeolog. Assoc, vol. xvi. (1900), p. 423. See also, Norman Collie
in Bristol Nat. Hist. Soc, 1879 : and, Mark Stirrup, Trans. Manchester Qeol.
Soc, vol. xxvi. (1901), p. 487.

t Geol. Surv., Summary of Progress for 1902, p. 60.

+ On the ores of this locality consult : " The ironstone Formation of the
Forest of Dean ; with a sketch of the General Geology and Industrial History
of the District." By Dr. J. W. Watson. The Geologist, vol. i. (1858), pp 217,
265. See also, Proc. Cotteswold Club, vol. viii., p. 32 ; vol. x., p. 220.

§ The smith-ore may yield from 54 to 58 per cent, of ferric oxide, whilst the
brush-ore may contain, when pure, 80 per cent

MINERALS OF SOUTH WALES. 117

The iron-ores of the Forest of Dean were worked certainly in the
Roman period, perhaps even earlier. Vast cinder heaps, or accumu-
lations of old slags, are still found in the Forest, and occasionally
declare their age by yielding a Roman coin or other characteristic
relic. The remains of the ancient workings are known as scowles*

Although ironstone-mining in this locality has declined in recent
years, it is by no means extinct. According to the Home Office
statistics the amount of brown iron-ore raised in the Forest of Dean
during the year 1902 was 5,738 tons.

Iron-pyrites occurs in masses, locally called " dogs," in a vein of
coal known in the Forest as the " Twenty Inches." A list of the
minerals of the Forest of Dean was published by the late Mr. W. H.
Fryer, of Coleford, in the Proc. Cottesivold Club, vol. viii., p. 32 ;
and a general list of the minerals of Gloucestershire was given by the
late Rev. Dr. Smithe, of Churchdown, in the same publication,
vol. viii. p., .'53.

Minerals of South Wales.
(Nos. 863 to 874).

A ■> in the little coalfield of the Forest of Dean, so in the vast field
of South Wales, the Carboniferous Limestone contains, at least along
the southern margin of the basin, occasional pockets of iron-ore, in-
cluding both the red oxide, or Hcematite, and the brown oxide, or
Li monitcf These ores occur in irregular deposits, often lying more or
less directly along the planes of bedding and jointing of the limestone
suggesting the introduction of the iron from solutions running along
the easiest path offered by any planes of weakness. In some cases
the ore appears to occur in the body of the limestone, as at the old
Garth Mine, at Pentyrch ; in others at the junction of the limestone
and the Millstone Grit shales, with Dolomitic Conglomerate above, as
at Mwyndy, near Llantrissant, where the ore also occupies vertical
fissures in the limestone ; and in other cases again the ore occurs
between the Carboniferous Limestone and the shales, and at the
junction of the Carboniferous strata with the overlying Dolomitic
Conglomerate, as at the Trecastle Mine. Mr. Stephen Vivian has
illustrated these several modes of occurrence. It often happens
that whilst the limestone forms the footwall, the shale may form
the hanging wall ; the grit being absent.

Specimens of the haematite, or red ore (Xos. 863, 864) show its
general resemblance to the ores of Ulverston and of Whitehaven
(p. 144), and any explanation of the origin of the one will probably
apply to that of the others. Some of the South Wales haematite is
highly siliceous, forming the stone called " blue ore." It seems to

* " The Forest of Dean ; an Historical and Descriptive Account." By
[Rev.] H. G. Nicholls, M.A. 1858.

■f See " The Haematite Deposits of the southern Outcrop of the Carboni-
ferous Limestone of South Wales." By W. StepheD Vivian. Trans. S.
Wales Inst. Eng., vol. xiv. (1884-86), p. 164.

Also Mr. Strahan's Geolog. Surv. Mem. on Geology of the Country around
Newport, 1899.

118 MINERALS OP SOUTH WALES.

have been suffused with siliceous solutions, and crystals of quartz
not infrequently are found lining cavities in the ore. No. 868 is a
specimen from the old Mwyndy mine, showing beautiful crystals of
quartz, colourless and limpid, with enclosures of limonite in the
form of parallel rods or needles. The ore is said to become less
siliceous in depth, and passes in some places into soft ochre.

Whether the source of the iron were the coal-measure ironstones, as
has been suggested, or, as seems much more likely, the red rocks of
the Dolomitic Conglomerate, or other Triassic strata, which probably
once covered much of the country, the iron seems to have been
carried downwards in solution, and to have partially replaced the
limestone. Probably ferrous carbonate was first formed, and this
subsequently converted into oxide. Chalybite, however, though
not unknown, is a mineral of exceptional occurrence here. The
formation of the ore by metasomatic replacement has been studied
by Mr. E. Wethered,* Prof. Howard f and Mr. A. Strahan. {

Conclusive evidence of the substitution of ferric oxide for calcite
in the limestones of South Wales is furnished by Mr. Strahan, who
has figured a microscopic section of Carboniferous Limestone from
Rhubina, in which organic structures, representing crinoids and
polyzoa, have been replaced by red oxide of iron.§

The specimen No. 869, presented by H. H. Thomas, Esq., shows
excellent crystals of ferriferous dolomite from the Lower Coal-
measure sandstone of Park Colliery, Tirydial, S. Wales.

Manganese ore has occurred at the Trecastle Mine and ores of lead
and cojjper are also found occasionally in the Carboniferous Lime-
stone ; whilst galena is by no means uncommon in the Dolomitic
Conglomerate. No. 865 is a specimen of galena, and No. 866 one
of copper-pyrites, both from the Carboniferous Limestone of
Mynydd-y-Gareg, Kidwelly, presented by E. E. L. Dixon, Esq.

The occurrence of galena in the coal-measures has been frequently
observed, not only in South Wales but in several other localities.
The late Mr. E. Rogers recorded a case in which a seam of coal in
the Pennant series at Abercarn was traversed by an impersistent
vein, consisting of iron pyrites, galena and calcite. The coal in the
immediate neighbourhood of the lode exhibited no evidence of the
action of heat,|| and the minerals were no doubt deposited in the wet
way. The unusual occurrence of galena in the underclay of a
coal-seam near Coed-Ely, has been noted by Mr. Strahan in the
Geol. Surv. Memoir on Pontypridd (p. 81).

* "On the Origin of the Haematite Deposits in the Carboniferous Limestone. "-
Geol. Mag. [N. S.] Deo. ii, vol. ix. (1882), p. 522.

-j- " The Haematite Deposits of South Wales and the Theories regarding
their Formation," Trans. Cardiff Nat. Soc, vol. xxvi., Part 1 (1894), p. 47.

% " The Geology of the South Wales Coalfield, Part 1. The Country around
Newport." By Aubrey Strahan, M.A., 1899.

§ Ibid. Plate, fig. B.

|| " On the occurrence of a metalliferous vein of lead, passing through a
coal bed in South Wales." Trans. South Wales Inst. Engineers, vol. i. (1859)
p. 228.

IRONSTONES. 110

Iron-pyriits is common in the Coal-measures of South Wales, as in
other coal districts. It occurs either as impure nodules and bands,
or as films on the joints and partings of the coal, or again dis-
seminated through the coal itself. It is often termed by miners
brasses, whilst pyritic seams are known as brass veins. Some of the
material so called in South Wales contains, however, but very little
pyrites, and the late Mr. W. Adams remarked that the Duffryn
Brass is really an iron ore with only a small percentage of pyrites.*
In addition to the ordinary form of ' visible yellow pyrites,' the
mineral also occurs so intimately associated with the coal as to
escape ocular observation, and in this state has been called
■ black pyrites.'f The specimen of pyrites in coal (No. 867) is from
near Kidwelly.

It is easy to understand how sulphide of iron might be formed in
the coal-measures by the reducing action of decomposing vegetable
matter on solutions containing sulphates with iron-salts. In some
cases its formation may have been contemporaneous with that
of the coal, but where the mineral occurs along the joints of the
fuel it must evidently have been of subsequent formation.

A large series of specimens of Clay-ironstone from the South Wales
coalfield is displayed in the Wall-cases 50 to 5-i.^ This ironstone is
a very impure form of ferrous carbonate, of variable composition but
containing 25 to 35 per cent, of metallic iron. It either occurs as
nodules called balls, distributed through the shales, or is spread out
as distinct beds or veins known as pins. By miners the stone is
generally termed mine — a word frequently applied elsewhere to ores
of iron. Although they have now lost much of their former
importance, these clay ironstones formed, during the first half of the
nineteenth century, the staple raw material of the iron industry of
the country. In some cases the ferrous carbonate of the coal-
measures is associated with much bituminous matter, and is then
known, from its colour, as black band ironstone.

It is not unlikely that the original source of much of the iron in the
coal-measures may be traced to the iron-bearing silicates of the
crystalline rocks. Such silicates may be decomposed even by
ordinary meteoric waters charged with carbonic acid. Under oxidis-
ing influences the ferrous carbonate would readily suffer alteration,
but by the reducing action of decomposing organic matter might
be retained in the ferrous condition. This precipitated carbonate

* " On the ' Coal Brasses ' of the South Wales Coal-fields," Trans. South
Wales Inst. Eng., vol. v. (1867), p. 190.

f See Mr. Strahan's Notes in Blue-book, Roy. Com. on Arsenical Poisoning,
vol. ii a903), p. 303.

\ For a description of the ironstones of South Wales see several memoirs
of the Geological Survey, viz : " The Ironstones of Great Britain," Part iii.
1861 ; Mr. A. Strahan's" " Geology of the South Wales Coal Field," Part i.
(Newport) 1899 ; Part ii. (Abergavenny) 1900 ; Part iv. (PoDtypridd and
Maes-teg) 1903. The origin of the clay iron ore is discussed by Sir H. T. De la
Beche and by Mr. R. Huntin vol. i. of the " Memoirs of the fJeological
Survey."

120 MINERALS OF SOUTH .. „„^.

might be mingled with the mud of the coal-measures or possibly be
introduced after it had hardened into shale. In the case of the balls,
an organism seems in many cases to have served as a nucleus,
and the impure carbonate has gathered round this centre of aggre-
gation, much in the same way as that in which the septaria of
other argillaceous formations have been formed (No. 870). Some of
the clay ironstone nodules show successive zones of concretionary
deposits around an organic nucleus. Nodules of iron carbonate are
known sometimes as Sphcerosiderite. Fissures of contraction may
occur in these nodules, as in ordinary septaria, and on the walls of
these cracks certain minerals have sometimes crystallised. The
specimen No. 871 shows crystals of quartz and calcite in the
shrinkage cracks of an ironstone from Merthyr Tydfil. Metallic
sulphides are also occasionally found in such situations ; and the
occurrence of such minerals as galena, blende and millerite, asso-
ciated perhaps with quartz, calcite and barytes, suggests the manner
in which certain mineral veins may have been filled. A series of
specimens illustrating these miniature ore-deposits is exhibited in
Wall-case 24.

Millerite. (Xo. 872.)

To a mineralogist the most interesting occurrence in the Coal
measures of South Wales is that of the rare mineral Millerite. This
is a sulphide of nickel, occurring in the form of delicate brass-like
needles or fibres in the fissures of certain clay ironstones, especially
in the neighbourhood of Merthyr Tydfil. The mineral is confined
to certain courses of ironstone, extending however, over a consider-
able area, especially the ores known locally as the " Three-quarter
Balls," the " Soap Vein," and the " Spotted Vein." In some cases
the filaments shoot across the cracks, from wall to wall, whilst in
others they are aggregated in divergent tufts. The specimen
No. 872 illustrates the behaviour of the mineral. Millerite is
known sometimes as nickel pyrites, whilst its capillary habit has
suggested the name of hair pyrites.

Nickel is an element which rarely occurs in quantity, though its
diffusion seems not to be so limited as was formerly supposed. It
has been detected, for example, by Mr. J. Pattinson in the Cleveland
ironstone ;* Dr. Pollard found it in a manganese deposit of culm-
measure age in Devonshiref ; it is known to occur in the manganese
nodules of the deep-sea floor ; and its presence is recorded by
M. A. Jorison, in the dust from chimneys and fluesf in places where
certain Belgian coal has been burnt. The nickel is usually accom-
panied, even if it occur only in traces, by cobalt ; but it may be said
generally that nickel is a more abundant element, so that when the
nickel and cobalt are associated the former usually dominates. Iron-
pyrites is sometimes nickeliferous, and this may represent the

* Rep. Brit. Assoc, for 1863, p. 49.

f Summary of Progress, Geol Surv., for 1899, p. 175.

J Ann. Soc. Oeol. Bdgique, vol. xxiii. (1895-6), p. 101.

HATCHETTIXE, ETC. 121

original form in which the nickel was, in many cases, introduced
into the rocks. At the same time, it is to be noted that nickel also
occurs in basic eruptive rocks, like peridotite, probably in the
olivine, whence it may pass, on their alteration, into the resulting
serpentine. In many localities nickel-ores occur in a serpentinous
matrix.

Hutrhettine uYos. ?7'o, fili).

Among the minerals occurring in the contraction- cracks of the
ironstone balls of South Wales one of the most remarkable is the
substance known as mitieral tallovj or HcUckettine (Xos. 873, 874).
This is a soft waxy hydrocarbon, often transparent when fresh, and
composed of thin yellowish laminae, of rather nacreous lustre, becom-
ing black and opaque on exposure. Scientific attention was first
called to it by Rev. J. J. Conybeare, who described it as occurring
in fissures in the clay iron-ore, associated with calcite and with small
crystals of quartz known as Merthyr Diamonds* It was analysed
several years afterwards by Prof. F. W. Johnston. f Conybeare named
it after Mr. Charles Hatchett, a well-known chemist of the early
part of the nineteenth century, who made a special study of
bituminous substances. J

A substance described as hatchettine, and therefore if not identical
with the mineral of South Wales at least presumably similar to it, has
been recorded from certain coal mines in the North of England, and
is said to have occurred at one time in such abundance at the South
Hetton Pit that the pit boys used it for greasing the axles of their
trams§.

Minerals of Mid- Wales (Nos. 875, 876).

Over a large part of Central Wales there stretches a complicated
series of contorted strata, consisting mostly of hard grits and slaty
rocks, imperfectly cleaved and generally unfossiliferous, but traversed
in many places by mineral veins. These veins are almost exclusively
confined, in Cardiganshire, to that part of the Silurian system
(Llandovery), distinguished by the late Mr. W. Keeping as the
Metalliferous Slate series.\\ No granitic rocks are associated with the
slates, and the lodes are not apparently connected with any igneous
intrusion. The general course of the veins is E.N.E and W.S.W.,

* '• Description of a new substance found in Ironstone." Ann. Phil, [new
ser.Lvol. i. (1821), p. 136.

-|- " On the composition of certain mineral substances of organic origin,
ii. Hatchetine («>)." Phil. Mag., vol. xii. (1838), p. 338.

+ Charles Hatchett was born in 1765. Conybeare ?p?]t the name of the
mineral Hatchetine, but Mr, Hatchett's name ended with a double '' t." (Nat.
Dirt, Biography, s. v.) Conybeare withdrew the name in favour of Brande's
term. Mineral Adipocere.

§ " On Minerals and Salts found in Coal-Pits." By R. Calvert Clapham
and John Daglish. Trans. N. Engl. Inst. Min. Eng., vol. xiii., 1864, p. 219.

" The Geology of Central Wales." Quart Journ. Qeol. Soc., vol. xxxvii,
(1831), p. 141. Also: Mr. Herbert Lapworth, ibid., vol. lvi. (1900), p. 67.
7882. K

122 MINERALS OF MID-W .*»..«.«-

but their direction is subject to much local variation, some veins
taking quite a zig-zag course, especially changing their direction
when the nature of the enclosing rock changes.*

The infilling of the veins is largely composed of brecciated slaty
rock, usually cemented by quartz, with more or less galena and zinc
blende. A fine series of brecciated veinstones, including many
examples from Mid- Wales, will be found in Wall-cases 31 and 32;

The principal ore is Galena, which in some cases is highly argenti-
ferous. Crystals of galena are not uncommon, and contrary to what
has been observed in some localities the boldly crystallised ore is
often not less rich in silver than the granular galena. Cerussite
occurs as an alteration-product of the galena, but is not of common
occurrence. Zinc blende is associated with the lead-ore, sometimes
even predominating, but Calamine is rare. Copper-pyrites often
occurs with the galena, though usually in very small quantity.
Iron-pyrites is found in certain localities in some abundance, but, on
the whole, is decidedly rare, and the general absence of pyrites
sufficiently explains the fact that the back of the lodes in Mid-Wales
is not usually marked by gozzan.

The common spar in the veinstone is Quartz, and the experienced
miner is in the habit of basing his opinion on the value of a given lode
by the character of the quartz. Colette occurs in much smaller
quantities, Barytes is by no means common, whilst Fluor-spar seems
to be altogether absent. Witherite, or carbonate of barium, has
been found locally.

Regularly banded veinstones are rare, and the minerals usually
occur in strings and irregular ramifications. Where the veinstone is
banded, it has been noted, according to the late Sir W. W. Smyth,
that quartz has been first deposited on the vein-wall, and then
followed by calcite. In like manner the galena in these ore-deposits
seems to have generally preceded the blende.

As an example of argentiferous galena, reference may be made to
No. 875, which is a specimen of finely granular ore from the Darren
Mine, near Aberystwyth, an ore that yielded an average of 32 Ozs.
of silver to the ton of lead. It has often been observed that lead-ore
is more likely to bear silver when occurring in slate or granite than
when in limestone or dolomite.

The lead- veins of Central Wales appear to have tempted the miner
at a very early period, as witnessed by the rude stone mauls and
dressing stones occasionally found in some of the old workings. It
was from the rich silver-lead mines of Cardiganshire that Sir Hugh
Myddelton derived the large fortune which he expended, in the early
part of the seventeenth century, in his great scheme for supplying
London with a source of water by cutting the New River. At a
rather later period, the mines of the " Welsh Potosi " were worked

* " On the Mining- District of Cardiganshire and Montgomeryshire." By
Warington W. Smyth, M.A. Mem. Geol. Surv., vol. ii., part 2 (1848),
p. 655.

VALES. 123

by Thomas Bushell, who by authority of Charles I. established a
mint at Aberystwyth for coining the bullion obtained from the
rich ore of the Welsh mines.*

At the present time the silver-lead ores of Mid-Wales are sub-
ordinate in economic importance to the zinc-ores. In 1902 the
mines of Cardiganshire, worked chiefly amid the romantic scenery
of the Devil's Bridge, yielded 3,618 tons of zinc-ore, but only 1,314
tons of lead-ore ; whilst Montgomeryshire turned out but 275 tons
of lead-ore and forty-five tons of zinc-ore. In Carmarthenshire 172
tons of lead were raised.

The Van Mine, near Llanidloes,the only lead mine in Montgomery-
shire, was at one time a most productive working. The lode which
was worked at this mine, as described by Sir Clement Foster,f ran in
a direction E. 26° X, and in some places was as much as forty-eight
feet in width. Its course could be traced through the slaty country
for a distance of nine miles. The lode was in many .parts a true
breccia, consisting of fragments of slate cemented by galena and
zinc blende. The Montgomeryshire lead-ore is represented by No.
876.

Minerals of Xorth Wales (Nos. 877 to 894).

Whilst certain minerals of Xorth Wales, such as the broohite of
Tremadoc and the anglesite of the Parys Mountain, are of much
scientific interest, there are many others which are, or have been, of
great industrial importance : such, for instance, are the ores of lead
and zinc from the Carboniferous strata of Denbighshire and Flint-
shire, and the ores of copper, manganese and gold from the older
palaeozoic rocks of the Principality. A few representatives of both
types of mineral are here grouped together.

Lea, I ,ui'l Zlnr Ores, etc. (Xo. 877 to 881).

Roman pigs of lead, with coins, fibulae and other objects of anti-
quity, testify to the early date at which the lead-ores of Xorth Wales
attracted the explorer. On the disintegration of the lead-veins at
their outcrop, masses of ore would be set free and might consequently
be found as water-worn lumps in the soil or in the drift ; in this way
were formed the deposits known as round ore or gravel ore. Much lead
was formerly obtained by driving levels in the drift-gravels, where
the ore was generally found resting, by virtue of its destiny, near the
bed rock. At the famous Talargoch mine, near Rhyl, the gravel ore
was at one time a source of much lead. Similar ore is known in
other lead-districts, as in the Mendips. The specimen No. 877 is a
rolled pebble of galena from Minera.

* See " Notices of the History of the Lead Mines of Cardiganshire." By
Robert Hunt. Mtm. Geol. Surv., vol. ii., Part ii. (1848), p. 635. Also :
Meyrick's " History and Antiquities of the County of Cardigan." 1810.

+ " Notes on the Van Mine." Trans. Boy. Geol. Soc. Corn., vol. x. (1879),
p. 33.

7882. • * 2

12 i MINERALS OF NORTH

At the present time the most productive mines in the Principality
are, for lead, the Halkin Mine near Holywell, in Flintshire, and for
zinc, the Minera Mine, near Wrexham, in Denbighshire.* The
occurrence of the ore-deposits in the Carboniferous strata of North
Wales has been described by Mr. Aubrey Strahan.f

Most of the veins which carry argentiferous galena and blende
run approximately in an east and west direction, whilst the cross-
courses, or veins which take a north and south course and appear to be
generally of later date, contain galena which is much less rich in
silver, and they bear no blende, though a little copper pyrites may be
present. The ore-bearing veins occur in the middle and upper beds
of the Carboniferous Limestone, and in the chert beds of the Millstone
Grit. The veins are most productive below certain beds of shale,
and Mr. Strahan has suggested that this may be due partly to the
shales having acted as " water-tight blankets, checking the flow of
underground water," and partly to the decomposition of the pyrites
in the shales having evolved sulphuretted hydrogen, which would
determine the precipitation of the sulphides of lead and zinc from
circulating solutions containing salts of these metals.

The veinstuff in the North Wales ore-deposits may be argillaceous,
siliceous or calcareous. Calcite is not uncommon, and occurs in
some cases in beautiful transparent masses, with rhombohedral
cleavage. Pennant, writing in 1796, refers to the Pen-y-bryn Mine,
near Holywell, as " remarkable for the quantity of refracting spar,
spatum Islandicum, of great purity and transparency ; and often
elegantly infected with marcasite finely disposed in lines. "J The
enclosed mineral may have been copper-pyrites, which occasionally
occurs in the form of needle-like crystals, forming bands in the spar.

The specimen No. 881 is an example of the fluor-spar sometimes
found as a veinstone at the Halkin Mountain. This example is of
p dark purple colour, and is crystallised in bold interpenetrating cubes.
No. 879 shows the zinc blende in small, transparent crystals of bright
brown colour, whilst No. 880 is an example of ruby blende, so called
from the beautiful colour, lustre and transparency of the small
crystals, which are here associated with dolomite, or pearl spar.

In the shallow parts of the lead-veins and zinc-veins in North
Wales, as elsewhere, the metals are often found as carbonates, form-
ing respectively Cerussite and Calamine. Some of the mines were
rich in cerussite, or white lead ore, where the veins passed through
rocks which, by their porosity, admitted free circulation of water,
bringing the galena under conditions favourable for alteration.
No. 878 is a specimen of Cerussite from the Jamacia Mine, in

* In 1902 thn amount of lead ore raised in Flintshire was 3,977 tons, and
in Denbighshire only 234 tons ; of this amount. Halkin yielded 2,316 tons. In
the same year the amount of zinc ore raised in Flintshire was 2,656 tons, and
in Denbighshire 3,239 tons, of which Minera yielded 3,218 tons.

t Mem. Geol. Surv. " Rhyl, Abergele and Colwyn." Quarter-sheet 79 N.W.
(1885) ; and " Flint, Mold and Ruthin." Quarter-sheet 79 S.E. (1890).

% " The History of the Parishes of Whiteford and Holywell," p. 254.

MA.NC.VNKSK OltKS. 125

Flintshire. Calamine was at one time so abundant that it was used,
in ignorance of its nature, for mending the roads ; and when its
value came to be recognised, the old roads were picked up for
sake of the mineral. Mr. Strahan remarks that calamine is known
locally as ' coke,' a word of uncertain origin, and not to be confounded
with eau-k, the common name of barytes.

In the lower beds of the Carboniferous Limestone, which are gener-
ally destitute of lead and zinc, iron-ore is not infrequently found in
the form of Hcematite. This has probably been formed from the
carbonate, which has replaced the limestone as a local substitution
product. More notable is the occurrence of nickel and cobalt, dis-
covered in 1*70 by Mr. Gage, at the Moel Hiraddug Mine, near Rhyl.
These metals occurred in the form of asbolan, a black, earthy ore
found as grains and lumps in a pocket or irregular cavity in the lime-
stone, containing clay and oxide of iron. The lumps contained in
some cases a core of pyrites, which was found to be cobaltiferous and
nickeliferous, thus pointing to the probable source of the asbolan.
The average assay of the black ore yielded 2-05 per cent, of cobalt
and 0- 75 of nickel. After having been worked for several years, the
output ceased in 1890. The occurrence of the mineral has been
described by Sir C. Le Neve Foster.*

Manganese Ores (No. 8*2).

Manganese occurred in the Flintshire cobalt-ore, and it has also
been found as oxide, in other localities in North Wales. The four
chemically related rretnls — iron, nickel, cobplt and manganese —
tend to occur in natural association, but in very unequal proportion.
Small quantities of nickel and cobalt may, however, be more widely
diffused than is generally supposed. Thus, Dr. Pollard found them
in a bluish black sand from the Reading beds of Cadmore End
Common. f

The specimen No. 882 represents an interesting occurrence of
manganese-ore, which is of some commercial importance in Merion-
ethshire and Carnarvonshire. An outcrop of black oxide of man-
ganese was worked many years ago in North Wales, but when
followed downwards this gave way to the carbonate, which was con-
sidered useless, and the workings were consequently abandoned.
Its value, however, came in due time to be recognised, and the ore
is now rather largely employed in the production of spiegeleisen and
ferro-manganese. In 1902 the amount of manganese ore raised in
Merionethshire was 027 tons, and in Carnarvonshire 531 tons. The
occurrence of the ore has been described by Sir Clement Foster!
and by Mr. E. Halse.§

* " On the Occurrence of Cobalt-ore in Flintshire." Trans. Boy. Geol. Soc.
Corn., vol. x., p. 107.

t Summary of Progress for 1900, p. 123.

% Rep. Brit. Assoc., Birmingham (1886), p. 085.

§ Trans. N. Engl. Inst. Min. Eng., vol xxxvi.. p. 103. " Note on the Occur-
rence of Manganese Ores near the Arenigs, Merionethshire." By Kdward
Hake. Trans. Fed. Inst. Min. Eng., vol. Hi., p. 940.

126 MINERALS OF NORTH WALES.

The manganese ore of North Wales occurs as a bedded deposit,
of an average thickness of eighteen inches to two feet, intercalated
among the Cambrian grits and conglomerates. It is also found
locally in pockets and fissures in beds of volcanic ash and porphyry.
The ore is mainly a mixture of impure Dialogite, or manganese
carbonate, with Rhodonite, or manganese silicate, and contains from
20 to 32 per cent, of metallic manganese. Near the outcrop it passes
rather abruptly into the black oxide, as seen in the specimen here
exhibited.

It seems probable that the manganese may have had its source in
the volcanic rocks which occur abundantly in North Wales, and
whence the manganese may have been leached out by acidulated
water and ultimately deposited as the carbonate, or dialogite.
The manganese in the well-known concretionary nodules found by
the Challenger, on the floor of the deep sea, is supposed to have been
derived from basic volcanic rocks. These nodules, of a dull brown
colour, formed of successive deposits producing a zonary structure,
consist of amorphous hydrated manganese oxides, rather indefinite
in composition, and mixed with variable quantities of limonite, clay
and other earthy matter.* They contain not only manganese and
iron, but also nickel and cobalt, illustrating the wide distribution
and intimate association of these elements.

Manganesiferous incrustations occur on sharks' teeth and bones
and on fragments of coral and rock found in deep-sea deposits. A
black incrustation consisting largely of manganese oxide is common
also on pebbles in river-gravels, and is often deposited by springs.
Whilst the carbonates of manganese and iron are isomorphous so
that they occur in chemical union in certain crystalline ores, the
hydrated oxides of the two metals are usually not crystallised and
occur only in a state of mechanical association, more or less distinct.f

The pisolitic iron-ore represented by No. 890 is an ore of bluish-
black colour, with magnetic properties, occurring as a band at a
definite horizon in the Arenig beds of North Wales.

Copper Ores (No. 887).

Copper-ores are rather widely distributed through North and
Central Wales, partly in the Carboniferous strata and partly in the
older palaeozoic rocks, but rarely concentrated in quantity. At the
present time the copper produced is but small. In 1902 the
Britannia Mine at Snowdon yielded 172 tons ; whilst eighty-four
tons were raised in Denbighshire, and sixty-five tons in Cardigan-
shire. No. 887 is a specimen of copper-pyrites from Snowdon.

The copper- ores of Snowdon, consisting of copper-pyrites in a vein-
stone of quartz, were described by the late Sir Andrew Ramsay as
occurring in lodes which represent faults. J In the early part of the

* Report of the Challenger, vol. ii., p. 374.

■f " The Chemical Relation of Iron and Manganese in Sedimentary Rocks."
By R. A. F. Penrose, jr., Journ. Geology, vol. i., p. 356.

% Mem. Oeol. Survey, vol. iii. " The Geology of North Wales." By A. C.
Ramsay, LL.D., F.R.S., 2nd ed., 1881, p. 158.

COPPER-ORES ANI> ANfiLESlTE. 127

last century, small lumps of green carbonate of copper were found
in a peat bog near Dolgelly, and led to a remarkable type of copper
working. Some Liverpool speculators pared off the turf, burnt it
in kilns, and obtained copper from the ashes. The Turf Copper
Mine was situated to the west of Dol-y-frwynog ; and when the
peat was exhausted attention was directed to the neighbouring
rocks, which are described as consisting of talcose schists, containing
iron- pyrites and copper-pyrites very sparsely scattered in crystals and
specks, but in which no distinct copper-lode could be discovered.*
It is probable that waters percolating through the rocks carried off
sulphate of copper from the oxidation of the diffused pyrites, and
that this solution draining into the bog became reduced by the
organic matter. Some branches of oak and birch were found more
or less impregnated with metallic copper.f

Large quantities of copper-ore were formerly obtained from the
Parys Mine and the Mona Mine, at Parys Mountain, near Amlwch in
Anglesea. The ores consisted of copper-pyrites, iron-pyrites and a
complex ore known as blue stone, containing the sulphides of lead,
zinc and copper, of which a specimen is here exhibited (No. 883).
Remains of old workings prove that activity must have prevailed
here at a very distant period, and indeed masses of smelted copper,
bearing Roman stamps, have been found in the neighbourhood.
The Parys Mountain takes its name from Robert Parys, who was
Chancellor of North Wales in the reign of Henry IV.{

Although copper-ore is not directly worked in Anglesea at the
present time, considerable quantities of copper precipitate are
obtained from the cupreous waters which drain through the old
workings and the refuse heaps. Scrap iron is introduced into the
water, which contains the copper as sulphate, and metallic copper,
or cement copper, is precipitated ; whilst the remaining liquid,
containing iron sulphate, yields on exposure to oxidising influences
an ochreous deposit, valued as a pigment. In 1902, 450 tons of
copper precipitate were obtained from the Parys Mountain, whilst
the output of ochre reached the amount of 3,310 tons.

Anglesite (Nos. 884 to 886).

It is from the Isle of Anglesea that the native sulphate of lead
takes its name of Anglesite. The mineral appears to have been first
recognised as a distinct species by Dr. Withering, who obtained it
from the Parys copper mine, where it seems to have occurred at
one time in some abundance. Several excellent specimens are here
exhibited as Nos. 884 to 886. These show the anglesite in the form
of small transparent crystals, belonging to the orthorhombic system,
seated on a dull matrix of gozzany limonite. When pure the

* Ramsay, Op. cit., p. 65.

f Trans. Oeol Soc, 2nd ser., vol. v. (1837), p. 214.

% For the geology of Parys Mountain see Ramsay, Op. cit. p. 248. Also ;
Trans. Manchester Oeol. Soc, vol. xiv. (1878), p. 357.

15S

JI1XEKALS OV NORTH \\

crystals are colourless, but they usually present a brownish yellow
tint by association with oxide of iron. Like many lead-bearing
minerals, anglesite has a peculiar lustre, inclining to adamantine.
By the oxidation of the mixed sulphides in the ore above water-
level, various sulphates might be produced ; and of these sulphates
that of lead would be the least soluble, and might therefore be pre-
served as a crystallised mineral whilst the sulphates of iron, copper
and zinc, once associated with it, would be carried off in solution. A
certain resistance to common solvents is a necessary condition for
the very existence of most minerals.

Brookite, etc. {Nos. 888 to 893).

Another interesting mineral from North Wales is Brookite, of which
some specimens of exceptional beauty are here exhibited as Nos.
888 to 889. Brookite is one of the three species formed by native
titanium dioxide, the others being known as anatase and rutile.
Levy distinguished it, in 1825, and named it after Mr. H. J. Brooke,
the mineralogist, who was joint author of Brooke and Miller's well-
known treatise (b. 1771, d. 1857).

Brookite, as seen in these specimens, is a hyacinth-red translucent
mineral, of almost adamantine lustre, crystallising in the ortho-
rhombic system, and appearing usually in thin crystals of tabular
habit, due to predominance of the macropinacoid the planes of which
exhibit in many of the specimens well-marked vertical striations. *
The mineral is associated with finely crystallised quartz and with
albite. It occurs on the walls of clefts in a quarry of eruptive rock
near Fronolen, on the road from Bedgellert to Snowdon. Its occur-
rence alsonear Pwllheli has been recorded by Mr. W. J. Harrison, jun.j

Titanium dioxide has been formed artificially by the reaction of
titanium fluoride and water-vapour. The process is therefore
exactly analogous to that which has yielded cassiterite : indeed,
stannic oxide and titanic oxide stand in close chemical rela-
tionship. Pneumatolytic action may thus be invoked as a
possible explanation of the genesis of brookite. Nor of brookite
only : for the other modifications of this trimorphous body, TiO.„
may, in some cases, have had a like origin. Hautefeuille found that
when the reaction between the titanium fluoride and steam was
effected at a red heat Rutile is formed ; at a temperature such as is
required for the volatilisation of zinc Brookite is produced ; and at a
temperature just below that at which cadmium may be volatilised
Anatase results.

It is worth noting that anatase occurs with the brookite of
Snowdon. Butile is found in the cavities of the clay ironstone of
Merthyr Tydfil, but there it is probably of quite different origin. It

* A pinaccid is a form consisting of a pair of similar parallel planer
named from ir[va% (pinax, u, board or slab).
| On,. Mag., Is94, p. , r >G7.

' M.,l_', Vj l^.

V2'J

Js well known that rutilc, and to a less extent anatase, are widely
distributed as microscopic constituents of slates, clays and other
sedimentary rocks (seep. 191).

Some of the finest crystals of British Quartz are obtained from the
neighbourhood of Snowdon. The examples here exhibited (Xos.
• s '.ll, SH2) show that while some of this quartz may be pellucid
as nx-k crystal, other specimens are slightly opalescent and may
acquire a certain whiteness and opacity, sufficient to justify their
suggestive name of milky quartz.

Xo. 8". i.3 is a specimen of the well-known Jasper of Carnarvon-
shire, which has occasionally been worked as an ornamental stone.

In the Horse-shoe Case will be found some fine examples of
Asbestos, or fibrous hornblende, a mineral which occurs as veins
in the rocks of Moel Hebog, near Snowdon, and has been used
industrially.

Welsh Gold (X<>. 894).

Mention has already been made (p. 18) in connection with the
Cornish tin-ore of the wide distribution in minute quantity of Xative
Gold. Scattered more or less sparingly through the quartz-veins in
many parts of Wales, the metal is set free on the disintegration of
these veins at their outcrop, and by its density tends to accumulate
in local depressions, after the associated quartz has been swept
away by running water. Keltic tradition, not unsupported by
archaeological discovery, points to the rather profuse use of Welsh
gold at a very remote period.* Xor is this unreasonable. The early
settlers in the country might no doubt find much gold in the alluvial
deposits, not necessarily because the auriferous veins were then
richer than they now are, but rather because the materials of these
veins had been subjected during long periods of time to natural pro-
cesses of washing and dressing, so that the produce of ages might be
found in a concentrated form.

If alluvial gold satisfied the wants of the prehistoric inhabitant
of what is now Wales, the Roman invader was bold enough to
attack the obdurate reef itself. Remains of workings, reputed on
high authority to be Roman, still exist at Gogofau, near Lampeter,
in Carmarthenshire, showing that gold was extracted with much
labour from the quartz-lodes. Iron-pyrites is the principal metallic
mineral, but free gold was detected by the Geological Surveyors.}

In modern times, much attention has been directed to the gold-
bearing rocks of Merionethshire, where veins of quartz, occasionally
with calcite, carry iron-pyrites, copper-pyrites, zinc-blende and
galena, associated with more or less gold. According to Sir A. C.
Ramsay, the lodes run through the Lingula flags and Cambrian grits,
especially in the neighbourhood of intrusive rocks, and in association

* Sec, for instance, an " Historical Account or an Inquiry into the Situation
of the Gold Alines of the Ancient Britons." Cambrian Register, vol. iii., p.31.

t Notes on the Gogofau, or Ogo-fau, Mine, near Pumpsant, Carmarthen-
shire." By Warington W. Smyth, M.A. Mim. (1ml. Sun:, vol. i. (lS4(i), p. 480.

130 WELSH GOLD.

with certain rocks of talcose character.* Sir W. W. Smyth pointed
out the interesting fact that the gold is accompanied by tetradymite,
or telluric bismuth — a mineral which occurs in companionship with
gold at several other localities. - ) - Many illustrations of the occur-
rence of Welsh gold will be found in Wall-case 14.

Attention was called in 1843 by the late Mr. Arthur Dean to his
discovery of gold at Cwm Eisen, a mine which had been previously
worked for lead .J This announcement led to extended search,
resulting in the detection of gold over a wide district, notably
between Dolgelly and Barmouth, and in the alluvial deposits in the
valley of the Mawddach. Operations were carried on at several
mines, some of which, like the Vigra and Clogau, were on lodes pre-
viously worked for copper. These workings, however, were con-
ducted for many years on a comparatively small scale, and were only
intermittently productive until Mr. Pritchard Morgan, returning to
Wales with a knowledge of gold mining acquired in Australia, under-
took operations of a bold character at Gwynfynydd. At the present
time gold mining is carried on at St. David's mine, formerly the
Clogau, near Dolgelly ; at Gwyn, formerly the British Goldnelds,
Gwynfynydd ; at Ffridd Goch, Dolgelly ; and at Cefn Goch,
Tynygroes. According to the official statistics, these workings
yielded during the year 1902 a total quantity of 29,953 tons of gold
ore, of the estimated value of £12,621. The amount of gold ex-
tracted from this ore was 4,181 ozs., and its value £14,570. These
returns show a serious decline in the output. Thus, in 1900 the
amount of Welsh gold obtained during the year was valued at
£52,147.§

Analyses by the late Mr. David Forbes showed that a specimen
of gold from the Clogau lode contained upwards of 9 per cent, of
silver, the native metal thus corresponding to an alloy of the com-
position Au 6 Ag ; whilst a sample of stream gold from the Mawddach
yielded as much as 18 • 99 per cent, of silver.|| When the proportion
of silver in native gold reaches 20 per cent., the alloy is called
Electrum. The association of the Welsh gold with iron-pyrites and
in some cases with brown ochreous oxide of iron resulting from the
alteration of the sulphide, suggests that here, as in so many other
localities, the precious metal may have been originally brought up,
from a plutonic source, with the pyrites and set free on its decom-
position.

* " On the Geology of the Gold-bearing district of Merionethshire, North
Wales." By Prof. A. C. Ramsay. Quart. Jour. Geol. Soc, vol. x. (1854),
p. 242. Also Geol. Surv. Mem. " Geology of North Wales," p. 59.

t " Gold Mining at Clogau, North Wales." Mining and Smelting Mag.,
vol. i. (1866), p. 359.

% Reft. Brit. Assoc. York (1844), p. 56.

§ " Mines and Quarries : General Report and Statistics for 1902." Edited
by C. Le Neve Foster, D.Sc, F.R.S. (1903), p. 210.

LI " Researches in British Mineralogy." Phil. Mag. (1867), p. 329.

MINERALS OP DERBYSHIRE. 131

DIVISION 2.
MINERALS OF DERBYSHIRE.

The Spars
(Xos. sy.j to %-2.)

Metal- mining in Derbyshire, though now declining in importance,
is a very ancient industry, which was directed originally to the
extraction of the ores of lead, and subsequently to those of lead and
zinc. The ores — consisting of the normal sulphides, galena and
blende, with their alteration-products — are associated in the ore-
deposits of Derbyshire with calcite, fluor-spar and barytes. Three
types of ore repositories are recognised — the rakes, the pipes and the
flats. These seem to represent fissures, varying in magnitude and
direction, in the Carboniferous Limestone, which forms the char-
acteristic rock in the mining districts of the county. Channels for
the passage of water through the limestone are formed by the planes
of jointing, bedding, and faulting ; and the solvent action of the
circulating liquid produces irregular cavities which may become
receptacles for ore. It is probable, too, that here as in many other
limestone districts, the ore may, in some cases, have been substi-
tuted for the calcareous rock by a process of molecular replacement.
The ore-deposits are said to be most numerous and most productive
in the upper part of the limestone, some of the richest bodies of ore
having been found immediately under the Yoredale shales.*

Interstratified with the limestones there are occasional sheets of
basic eruptive rocks, usually olivine-dolerites, known locally as toad-
stone, and in many cases representing contemporaneous lava flows.")*
The old belief that the mineral-veins disappear in the toadstone
has often been disproved, though it remains a fact — subject, however,
to occasional exception — that the veins tend to become thinner and to
suffer impoverishment when they pass into the igneous rock. It is
generally held that the toadstone owes its name to its barren
character, the word being a corruption of Todtstein, or " deadstone."
German miners, or as old writers sometimes call them, " Dutch
mineral men," were occasionally brought over to this country for
the sake of their expert knowledge, and it is not unlikely that they
should apply such a name to a rock in which the ore died out.

The Rakes, or Rake veins, of the Derbyshire mines are deposits in
fissures representing joints in the limestone, more or less vertical in
direction, and sometimes corresponding with faults. The ore occurs

* On the Geology of the district and on the Occurrence of the Ores, see
Mem. OedL. Surv. " North Derbyshire." By A. H. Green, C. Le Neve
Foster, and J. R. Dakyns. 2nd Ed. (1887). By A. H. Green and A. Strahan.

f See " The Ancient Volcanoes of Great Britain." By Sir Archibald
Geikie, F.R.8. (1897), vol. ii., p. 8. And important papers by Mr. H. H.
Arnold-Bemrose in Quart. Journ. Qeol. Soc., vol. 1. (1894), p. 603; vol. lv.
(1899), pp. 224, 239.

l-'tt MINERALS OF DERBYSHIRE.

either in parallel ribs, alternating with bands of veinstuff, or in
isolated masses scattered through the sparry matrix. The term
serin is applied to a string, or small rake ; and in some cases a mass
of limestone may be traversed by a network of these veinlets, con-
sisting of galena.

Much of the lead-ore occurs, however, in the so-called Pipes, or
pipe veins, which are deposits in cavities widened by erosion in the
inclined direction of the beds of limestone, and connected one with
another by means of leaders running along joints. Another mode
of occurrence is that of Flats or flat veins, a name given to irregular
sheet-like masses of ore disposed along the planes of bedding.

It is found convenient to exhibit the metallic minerals in the
following Case, No. VIII., so that the series in Case VII., now under
notice, is limited to the three sparry minerals which form the
principal veinstuff of the Derbyshire deposits — namely cole spar, or
calcite, fluor-spar, or fluorite, and heavy spar, or barytes.

Calcite {Nos. 895 to 938).

Where ore-deposits occur in limestone, like those of Derbyshire,
Calcite is likely to be a common mineral, crystallising in any free
cavity, whether in the veinstone or in the neighbouring rock. Some
of the finest known crystals of this species have been brought to
light from the lead-mines of Derbyshire. A rather extensive series of
specimens is here exhibited, sufficient to give some notion of their
beauty and variety of form, but the specimens are necessarily of
small size, and the visitor should consequently turn to the Horse-
shoe Case (Section I.) in order to realise the magnitude attained
by some of the Derbyshire crystals, especially the large yellowish
scalenohedra.

Calcite presents an unparalleled wealth of crystalline forms. The
most characteristic of the Derbyshire crystals have a scalenohedral
habit, and are known from their sharp-pointed extremities as Dog-
tooth spar (Nos. 895 to 906). The scalenohedron is a solid bounded
by twelve scalene triangles, and having the lateral edges rising
and falling in a zig-zag manner, like those of a rhombo-
hedron. Other crystals assume a prismatic habit, the six-sided
prism being often terminated by the faces of a rhombohe-
dron or of a scalenohedron (Nos. 907 to 910). In some cases, as
in No. 911, the crystals are very complex, being highly charged with
faces. Twin crystals are of frequent occurrence. It is not uncommon
in Derbyshire specimens to find scalenohedral crystals having
re-entrant angles, producing notches in the equatorial belt, showing
that the scalenohedron is twinned on the basal pinacoid (No. 897).
But the most interesting twinned crystals are those found many
years ago at Eyam and known as butterfly twins (No. 917). These
are in some cases quite heart-shaped, constituting the type
which de Bournon called " la charmante made " — " chaux
carbonatee en coeur." * They are scalenohedra twinned on a plane

* "Traite de Mineralogie," vol. ii. (1808), p. 06.

UALiV.1 1 fi.

i:J3

of the rhombohedron. The Eyam twins are rather rare in collec-
tions, but similar crystals of larger size have been discovered in
recent years in the haematite mines of the North (p 149), and
are comparatively common.

Whatever the form assumed by calcite, the crystal always offers
perfect rhombohedral cleavage. No. 912 is a cleavage rhombo-
hedron ; but this fundamental form is rarely assumed independently
by British calcite, or for the matter of that, by any calcite, except
that from Iceland. The cleaved specimen No. 912 presents a
delicate yellow colour, due probably to the presence of iron. In the
columnar crystalline specimen No. 932 the yellowish colour is very
pronounced, giving the substance the tint of sugar candy. Most
of the Derbyshire calcite, however, is colourless or dead white. The
opaque white spar from some of the mineral-veins in Derbyshire is
crushed, and employed for making paths.*

Cavities in the fossils of the carboniferous limestone are sometimes
lined with beautiful crystals of calcite. No. 933, for example, is a
Derbyshire specimen, showing a crop of such crystals, studding the
inner shell- wall of the valve of a Productus. Another example is
furnished by No. 934.

The specimen of stalagmite, or dripstone, No. 935, illustrates the
formation of a calcareous deposit, in layers, from solution in water.
Meteoric waters, charged with carbonic acid, filter through the
limestone and drain along the planes of jointing and bedding, dis-
solving the rock by forming a soluble acid calcium carbonate, or
bi-carbonate of lime. The loosely associated carbonic acid is readily
eliminated from this compound, by elevation of temperature, or by
exposure to air, or by the action of living vegetation, and the cal-
careous salt is thereby reduced to the condition of the normal or
neutral carbonate, which is but very sparingly soluble in water, so
that it is easily precipitated. In recent years much attention has
been given to organic action in determining the deposition of cal-
careous matter ; and the researches of Dr. Cohn, Mr. W. H. Weedf
and others tend to show that algous growths and other forms of
plant life are frequently instrumental in causing precipitation, even
in the calcareous sinter of hot springs. No. 937 is a specimen of
tufa encrusting Chara, deposited by the calcareous waters of Matlock
in Derbyshire. It should be added that organic acids, derived
mainly from decomposing vegetable matter, greatly assist in the
solution of limestone-rocks.

Some of the coral-like deposits of carbonate of lime, like No. 938,
consist of Aragonite. It is generally held that the temperature at
which deposition occurs is an important factor in determining
whether the deposit shall take the form of calcite, or of the harder
and denser aragonite. This subject will be again referred to (p. lot')).

* Mem. Geol. Snrv., North Derbyshire (1887), p. 163.

t " Formation of Travertine and Siliceous Sinter by the Vegetation of Hot
Springe." By Walter Harvey Weed. Ninth Ann. Hep. U.S. Gcol. Surv.
(1*80), p. 613.

13-1 MINEBALS OF DERBYS? ; --

Dr. G. P. Merrill has shown that many stalagmitic deposits com-
monly regarded as aragonite really consist of carbonate of lime in
the normal form of calcite.*

Elaterite, etc. (Nos. 939 to 942).

The curious soft substance represented by No. 939 is known as
Elaterite, elastic bitumen or mineral caoutchouc — names which are
sufficiently suggestive of its characters. It appears to have been
first noticed about the year 1786 at the Odin Mine, near Castleton, one
of the oldest mines in the country. Scientific attention was not
called to it, however, until 1797, when Mr. C. Hatchett, who had
made a special study of bituminous minerals, described it as a new
species of bitumen, much resembling in elasticity and colour " the
substance known by the name of cahoutchou (sic), or india-rubber."f
According to Prof. J. W. P. Johnston, who analysed three specimens
from Derbyshire, the origin of the substance is probably attributable
to the effect of heat exerted by igneous rocks on the organic matter
of the Carboniferous Limestone, whereby volatile products were
evolved and condensed in the cooler rocks.J The substance has also
been found near Windy Knoll.

In the specimens Nos. 941, 942, hard brittle bitumen, or asphalt, is
seen occurring in the form of small globular masses, with dog-tooth
calcite, and blende, on fluor limestone. The form of this asphalt
suggests that it represents solidified drops of a substance once
liquid. Petroleum, or rock oil, sometimes oozes from the rocks, and
explosive gases have often occurred in the lead mines. §

Such bituminous substances, representing probably the organic
matter of the Carboniferous rocks, invite the suggestion that they,
or kindred substances, may have played some part in the process of
ore-formation by acting as reducing agents, and thus determining the
formation of metallic sulphides, like galena, blende and pyrites,
from solutions of the sulphates. The importance of bituminous
substances, and even of the small proportion of organic matter in
limestone, as reducing agents in the formation of ore-deposits, has
been recently insisted on by Dr. W. P. Jenny.||

Fluorite (Nos. 943 to 954).

In connection with the fine specimens of Fluorspar, or fluorite,
from the West of England mines, exhibited in Case V. (p. 85), so
much has already been said about this species that the Derbyshire

* " The Onyx Marbles,". By George P. Merrill. Rep. U.S. Nat. Mus. for
1893 (1895), p. 539.

f " Observations on Bituminous Substances, With a Description of the
Varieties of the Elastic Bitumen." Trans. Linn. Soc, vol. iv. (1797), p. 129.

X "On the Composition of Certain Mineral Substances of Organic Origin. V.,
Elastic' Bitumen of Derbyshire." Phil. Mag., vol. iii. (1838), p. 22.

§ Qeol. Surv. Mem., North Derbyshire, p. 164.

|| "The Chemistry of Ore-lieposition." Trans. Am. Inst, Min, Eng vol
xxxiii. (1903), p. 445.

-°"T T " m ^*v~- _„-,_ 135

specimens displayed in this part of the Collection call for little
remark. The spar occurs in many of the lead-mines as a gangue-
mineral, or constituent of the vein-stuff, and is raised to a limited
extent for use as a fluxing agent in metallurgical operations (whence
indeed its original name, from fluo, to flow). It is also employed in
the manufacture of a milky glass, in the production of hydrofluoric
acid for etching glass, and as a source of various fluorine-compounds
for laboratory use ; nor must its value as an ornamental stone be
forgotten. In the year 1902 1,297 tons of the spar, valued at £1,584,
were raised in Derbyshire.

Of all kinds of Derbyshire spar the most beautiful is the purple
fluor known as " Blue John," a name apparently correlative with
" Black Jack," the miners' common name for zinc-blende. The
specimens here shown illustrate the colour and structure of this spar
(Nos. 953, 954). It is found almost exclusively near Castleton at the
famous " Blue John Mine," situated on the side of Tray Cliff, in the
midst of the wild scenery of the Peak. It is generally found in
nodular masses, with a fibrous and concentric structure, enveloped
in a clayey matrix occupying a fissure or pipe. The clay may re-
present the insoluble residue left by removal of the limestone in
solution.*

The dark brownish purple fluor is called by the workmen " bull
beef," but the colour is greatly altered, and a beautiful amethystine
tint produced, by exposure to heat or by other artificial treatment.
Where the spar crops out in the rocks, the " changing " is effected by
the natural heat of the sun, and the dark blue fluor acquires a purple
colour. The spar at the Blue John Mine was first found by two
miners named John Kirk and Joseph Hall ; and its use for orna-
mental purposes dates from about 1770, when it was introduced by
Mr. Robert Hall, of Castleton. f

Many specimens of polished fluor from Derbyshire, including some
fine vases, will be found in the Hall of the Museum. The grand
amphora on a pedestal at the northern end of the Principal Floor
(No. 27), presented by the late S. Addington, Esq., is believed to be
the largest specimen of its kind in existence, measuring as it does as
much as two feet eight inches in height. It was the work of Mr.
Vallance, of Matlock.

Barytes (Nos. 956 to 960).

Sulphate of barium, forming the mineral known as Barytes, is very
common as a matrix of galena in lead-veins which traverse lime-
stone. Although it occurs as a gangue-mineral in Derbyshire it is
rarely crystallised, and as far finer specimens are exhibited from the
North, especially from Cumberland, any detailed notice of the species
may be suitably deferred (see p. 168).

* Oeol. Sum. Mem., North Derbyshire, p. 162, where a figure illustrates
the occurrence of the Blue John.

f " Gem of the Peak : Part V., History of the Fluorspar, Ancient and
Modem." By W. Adams. 4th Ed., 1845.

136 MINERALS OF DERBYihiKi.

Barytes is extensively used as a white pigment, and in 1902 Derby-
shire yielded 334 tons of the mineral. This consists principally of
the white earthy barytes known as cawk or caulk.

Some notable varieties of barytes occur in Derbyshire. A white
arborescent barytes, with brown earthy oxide of iron, formerly found
at Bonsai Moor, was known from its form as brainstone. No. 959
is a curious black variety of barytes, containing, according to an
analysis by Prof. G. A. Kcenig, 3 - l per cent, of oxide of manganese.*
The remarkable stalactitic barytes, found in every mineral collection,
is illustrated by Nos. 956 to 958. This variety was first found in
1832, embedded in clay in a cross course on Arbellow, at Middleton,
near Youlgreave. Transverse sections exhibit a beautiful radiated
structure, with well-marked concentric rings, suggestive of the section
of an exogenous tree stem ; and this structure, coupled with the rich
brown colour, has led to its being popularly called " fossil oak."
The zonal pattern displayed in section has also led to the rather
unfortunate name of " onyx stone." It is used to a limited extent
when cut and polished, as an ornamental stone, especially as a
material in inlaid marble work.

Quartz (Nos. 961, 962).

Quartz is by no means common among the minerals of Derby-
shire. f But in the neighbourhood of Buxton there are small crystals
of quartz, generally found loose in the soil, and known as Buxton
Diamonds. As seen in No. 961, the crystals present the form of
hexagonal prisms, terminated usually at each end by a hexagonal
pyramid. Whilst some are perfectly colourless, others are tinted
brown, with oxide of iron. They appear to have been derived from
such a source as is represented by No. 962, a specimen which shows
similar doubly-terminated crystals in a matrix of flesh-coloured
barytes.

* Proc. Acad. Nat. 8c. Phil, for 1878 (1879). p. 99.

f On quartz, see paper " On the Super-position of Quartz Crystals on
Calcite in the Igneous Rocks occurring in the Carboniferous Limestone of
Derbyshire." By W. F. Holroyd and J. Barnes. Trans. Blanch. Oeol. Soc,
vol. xxvi. (1901), p. 46.

LE.AD-OliES. ].'.,

ca.se viii.
division 1.

MINERALS OF DERBYSHIRE.

The Ores.

Gale ita (Xos. 963 to 986).

In this division of the Collection there is a fair display of the
ores of Derbyshire, chiefly those of lead and zinc. Some of the
lead-mines have yielded crystals of Galena exceptional in magni-
tude and beauty. Thus, the Mill Close Mine, in Darley Dale, at
present the most productive mine in Derbyshire, has furnished cubes
of galena measuring two inches along the edge, with dog-tooth spar
measuring a foot along the vertical axis of the scalenohedron.* The
occurrence of fine crystals lining hollows in the veinstone, or
studding the walls and roof of fissures in the limestone, suggests
the deposition of galena in free cavities ; though its formation by
molecular replacement of a calcareous rock is also to be frequently
recognised where ores of lead and zinc occur in limestone (p. 164).

The crystals of Derbyshire galena here exhibited show the mineral
in cubes and octahedra, but mostly in combinations of the two forms,
or cubo-octahedra. Some of the specimens present the characteristic
cubic cleavage, and in No. 971 the cleavage face is marked diagon-
ally by striations due to twin lamella?. The very brilliant metallic
lustre of galena, which has led to its being called " the diamond
among ores," is well displayed by such specimens as Xo. 972 ; but
the lustre is usually lost on exposure, and in some cases the tarnish
is brilliantly iridescent, as in Xos. 968, 969. Galena, in consequence
of its lustre, is sometimes known as Lead glance.

The coarsely-crystalline galena, generally considered, though
sometimes erroneously, to be poor in silver, is known from its use
in glazing pottery as potters' ore.f The amount of lead ore, princi-
pally galena, raised in Derbyshire in 1902 was 3,555 tons.

* " The Deposit at the Mill Close Lead Mine, Darley Dale, Matlock."' By
Cyril E. Parsons. Tram. Fed. In.it., vol. xii. (1896), p. 11.5.

t On the Continent this ore is known as alrjuijoux — a word which is
derived, as Prof. Bauerman has pointed out, from the Italian archijoglio, or
" large-leaved," being the name applied to it in the Levant trade. The ore
is exported to Egypt as a remedy in ophthalmia and for painting the eyelids.
The Arab name is kohlhe, whence it is known in parts of Spain, where it is used
in potteries, as alcohol. " The Metallurgy of Lead." By John Percy, M.D.,
F.R.S., 1870, p. 94.

7882. L

138 MINERALS OF DERBYSHIRE.

In the specimen No. 982, the smooth surface of the galena presents
a natural polish, and is known as a slickenside. This polish is the
result of friction due to movement in the vein, and the direction of
movement is indicated by the grooving or fluting seen on the face of
the stone. It is remarkable that some of the Derbyshire slickensides,
on being struck with a pick, will explode with more or less violence.
The molecules of the rock appear to be in a condition of severe strain,
like those of a Rupert's drop, so that the slightest breach of con-
tinuity at one spot, such as may be produced by a mere scratch, will
disturb the unstable equilibrium and lead to disruption throughout
a considerable mass. The subject of explosive slickensides has been
studied by Mr. A. Strahan.*

Many of the specimens in this case illustrate the characteristic
associates of galena. In No. 983 the galena occurs with calcite ; in
No. 984 with nuorite ; in No. 985 with barytes ; and in No. 986 with
blende. The occurrence of galena with the minerals resulting from
its own alteration, like cerussite and anglesite, is illustrated in the
following series.

Cerussite (Nos. 987 to 990).

The formation of Cerussite, or carbonate of lead, from galena is
illustrated by several specimens in this Case (Nos. 987 to 989),
where the two minerals are intimately associated, whilst the galena
shows in some cases, by its eroded surface, that it has suffered much
alteration. Frequently the carbonate occurs as a white, earthy
incrustation on the weathered galena near the back of a vein. Re-
garded formerly, according to Farey, as a useless spar, it was either
left in the mines or thrown away and buried in the hillocks. At
times it has been rather extensively worked under the name of
white ore or wheat stone, and a vein at Tideswell Moor has received
the name of the " White Rake," in consequence of the occurrence
of this mineral.

The direct oxidation of galena might be expected to give rise to
anglesite rather than to cerussite, since the sulphide would become
converted into sulphate ; but the reaction of this sulphate with the
limestone would result in the formation of a carbonate. The
action of carbonated waters on galena in a limestone matrix invari-
ably produces cerussite ; and hence masses of galena, more or less
altered to impure white ore, or ' lead earth ' (Bleierde), are often
found in ore-deposits, within reach of surface drainage.

The fine prismatic crystal of cerussite, numbered 990, is dull and
blackened on the surface. Such discolouration is probably due to
the formation of a thin layer of black sulphide, consequent on
attack by sulphuretted hydrogen. This product is often evolved
from decomposing sulphides. Moreover, the sulphur compounds
emitted by blasting operations in mines tend to blacken any white
lead-ore in their neighbourhood.

" On Explosive Slickensides." Oeol. Mag., Dec. 3, vol. iv. (1887), p. 460.

LEAD-ORES. 139

Angle-site, etc. (Xos. 991 to 994).

Wherever galena has suffered oxidation, but has been shielded
from the attack of carbonates, Anglesite, or sulphate of lead, may be
expected to occur. Although in limestone districts it is naturally
not so common as cerussite, fine crystals have occasionally been
yielded by the lead mines of Derbyshire. Of these, several ex-
amples are here shown (Xos. 991 to 993). The characters of the
species have already been described in connection with the original
occurrence in Anglesea (p. 127).

It is worth noting that although galena and blende occur together
in the Derbyshire mines, the products of their oxidation present
marked differences. Sulphate of lead is very sparingly soluble in
water whilst sulphate of zinc is freely soluble. Hence the lead com-
pound remains as a fairly stable mineral, whilst the zinc salt i3
carried off in solution and is rarely found in a solid form. Goslarite,
or sulphate of zinc, though not unknown in stalactitic forms in
certain mines, may be practically ignored as a British species.

Specimens of lead- ore from the refuse-heaps of an old mine near
Brassington were collected by Sir H. T. de la Beche, to illustrate the
alteration of galena by prolonged weathering, and were described
in his Geological Observer (p. 692). Several of these specimens are
exhibited in Wall-case No. 35. They show the galena encrusted
with cerussite and pyromorphite — that is to say, the sulphide has
been more or less completely converted into carbonate and phos-
phate. The brown phosphate is known as linnets, and the green as
green linnets. No. 994 is an example of these alteration-products
from the Brassington hillocks. The name of " Green Linnets '' was
given to the mine which yielded these specimens.

Matlockite and Phosgenite or Cromfordite (Nos. 995 to 1006).

Derbyshire has contributed to the group of plumbiferous minerals
two rare and interesting species, which have been called, from their
original localities, Matlockite and Cromfordite. Both minerals
contain lead in the form of chloride, associated in the former with
an oxide, and in the latter with a carbonate of lead. Such at least
is the common interpretation of their constitution. Again, both
crystallise in the tetragonal system ; but whilst the crystals of
matlockite usually have a tabular habit, due to development of the
basal pinacoid, those of cromfordite, though sometimes tabular, have
generally a prismatic habit.

With regard to the names of these two species it may be remarked
that whilst matlockite is the name universally used to designate the
oxychloride, the term cromfordite, proposed by Greg and Lettsom
for the oxycarbonate, and locally appropriate, has given place, in
most quarters, to Breithaupt's name Phosgenite,* which, notwith-
standing its rather fanciful origin, has survived by right of priority.

* Phil. Mag., ser. 4, vok ii. (1851), p. 120.

140 MINERALS OF DERBYSHIRE.

The fine series of specimens of matlockite, Nos. 995 to 1002,
illustrate the typical characters of this mineral, showing the
yellowish adamantine tabular crystals, in some cases slightly curved
and aggregated in groups with a tendency to a globular form. The
mineral is identical in chemical composition with the white pigment
at one time largely prepared under the name of Pattinson's oxy-
chloride of lead.* Matlockite has been found among the sublima-
tion products of Vesuvius ; but its occurrence in Derbyshire suggests*,
of course, quite a different origin, and rather recalls the mode of
formation of mendipite — another oxychloride of lead already noticed
in connection with the minerals of Somersetshire. The relation of
matlockite and mendipite is seen by comparison of their formulae :

Matlockite ... Pb Cl 2 . PbO.

Mendipite ... Pb Cl 2 . (Pb0) 2 .

Phosgenite is represented by a fine suite of specimens (Nos. 1003
to 1006), including some beautiful transparent crystals, faintly
yellowish in colour and adamantine in lustre. The formula of the
species may be written Pb Cl 2 . Pb COj. It has been found naturally
altered to Cerussite, a change obviously brought about by removal of
the molecule of lead chloride. Phosgenite has been found in the
neogenic deposits of Bourbonne-les -Bains, and in the old slags of
Laurion, where the chlorine has been supplied by the sea-water.

Soluble chlorides reacting with carbonate of lead, dissolved
by carbonic acid, might give rise to such a chloro-carbonate as
phosgenite. The artificial production of this. species was effected
by MM. Friedel and Sarasin, by heating a mixture of chloride and
carbonate of lead with water in a closed tube at a temperature of
180°. With regard, however, to the Derbyshire mineral, which
was produced by the alteration of galena, there is no reason to
suggest for its production an elevated temperature. It is therefore
interesting to note that M. A. de Schulten has effected the synthesis
of crystallised phosgenite at ordinary temperature by passing a
current of carbonic acid gas through an aqueous solution of chloride
of lead.f

Both matlockite and phosgenite were originally found in old
workings in the lead mines near Cromford, not far from Matlock.
The locality given for phosgenite was the Boge Mine, in the little
village of Bole Hill. The chlorine in these minerals may possibly
have been derived, as suggested with regard to mendipite (p. 109),
either from neighbouring saliferous rocks now removed or more pro-
bably from surface-waters carrying a small proportion of chlorides.

Blende (Nos. 1007 to 1010).

In Derbyshire, as in so many other localities in limestone rocks,
the ores of zinc occur in intimate association with those ol lead.

* Percy's " Metallurgy of Lead." 1870, pp. 79, 81.

t " Sur la production artificielle a la temperature ordinaire de la Phos-
g3U : te." Par M. A. de Schulten. Bull. Soc. Fr. Min., vol. xx. (1807), p. 191

LEAD ANT) ZINC ORES. 141

The principal zinc-ores are the sulphide and the carbonate, the
latter being in most cases a secondary mineral derived from the
former.

Whilst the native sulphide is commonly known as zinc blende, or
simply blende, it is nowadays frequently termed by mineralogists
sphalerite — a name due to Haidinger, who, in the year 1845, intro-
duced it as a scientific word having much the same meaning as the
vulgar name " blende " ;* that is to say, it indicated the deceptive
character of the mineral which had led to its occasional confusion
with galena. The same idea is conveyed by the miners' terms
mock ore, false lead, or black Jack.

In deposits of mixed lead and zinc-ores the lead is likely to occur
in the upper part and the zinc below ; and for this and other reasons
the working of zinc-ore in a given district is often of comparatively
recent date. Blende is less stable than galena, so that in the zone of
oxidation it will be first attacked ; and moreover, the zinc sulphate
by reason of its greater solubility is so much more mobile than the
lead sulphate that it will tend to move downwards, where it may
be reduced to a less soluble form.

Some of the specimens show the blende in association with cubes
of fluorspar (as No. 1008) ; and in specimen (No. 1009) it is crystal-
lised with fluor in a fossil shell. The dark colour of common blende,
whence the name " black " Jack, is due to iron, probably in the con-
dition of FeS, a compound which occurs as a cubic mineral in
meteorites, and is known as Troilite. The ' rosin blende " is paler.

At the present time the only mine in Derbyshire raising zinc-ore
is the Mill Close Mine, in Darley Dale, which yielded 538 tons of
ore in 1902.

Calamine, etc. (Nos. 1011 to 1018).

Solutions containing zinc, such as those resulting from the altera-
tion of blende, are apt, on percolation through limestone, to form
carbonate of zinc, or calamine ; and since this body, unlike its
isomorph, ferrous carbonate, is characterised by much stability, the
metal may remain fixed in the form of carbonate.

Zinciferous solutions, by slowly attacking limestone, may effect
the gradual substitution of zinc for calcium, and thus give rise to
metasomatic deposits of calamine. In No. 1012 crystals of Derby-
shire dog-tooth spar have suffered partial alteration, and show a
thin external crust of calamine. The same kind of crustal alteration
has roughly affected the two bold scalenohedra in No. 1013. The
next specimen, No. 1014, shows that the calcite has been partially
dissolved away beneath the calamine, so that a thin shell of the zinc
carbonate is separated by a solution-space from a nucleus of un-
altered calcite. In No. 1015 all the calcite has disappeared, leaving
nothing but a thin shell of calamine representing not only the

* Sphalerite from oQaXtpbe (sphalercs) deceptive ; Blende from Ger.
blenden, to dazzle or to blind.

142 MINERALS OF DERBYSH1KB.

external form of the scalenohedral calcite but even the direction of
the cleavage-planes along which the calamine has penetrated.
Pseudomorphs of calamine after dog-tooth spar have attracted the
attention of observers from the days of Pilkington, more than a
century ago.*

With regard to the origin of calamine, it has been objected that
the reaction of carbonate of lime on a solution of sulphate of zinc
tends to precipitate the zinc as a hydrocarbonate. It is true that
the anhydrous zinc carbonate is not thrown down in laboratory
reactions, but M. Lodin has argued that under natural conditions
there are various ways in which the anhydrous salt might be precipi-
tated, especially by the presence of an excess of carbonate of lime,
such as exists in a limestone district. t

The series of Derbyshire minerals is brought to a close by some
specimens of pyrite andmarcasite (Nos. 1019 to 1022), which scarcely
call for special remark. The marcasite in No. 1021 shews the
form called "spear-head pyrites," and in No. 1022 that known as
" cock's- comb pyrites," the mineral in both specimens having
suffered epigenic alteration to limonite.

Minerals prom Bcton.
{Nos. 1023 to 1030.)

A few specimens from the famous copper-mine of Ecton are here
exhibited, for though Ecton is topographically within the borders
of Staffordshire, it is closely related geologically to the adjacent
part of Derbyshire. It is known that this mine was worked by
German miners brought over by Prince Rupert in the seventeenth
century, and that they introduced into this country the practice
of blasting. At one time the Ecton mine was described as "perhaps
the richest copper mine in Europe." J

According to Dr. Watson, writing in 1860,§ the ores occurred
in veins and saddles. The copper-ore was mostly found in the
saddles, the mineral occurring in the arches of sharply folded
Carboniferous Limestone, whilst the pipe-veins and rake-veins
usually carried galena with a small quantity of blende. Mr. W.
Bowman, the manager of the Ecton Company, which started fresh
workings in 1883, describes the mine as essentially a " pipe work."||
As a rule, galena was found in the higher levels and copper-ore

* Geol. Surv. Mem., " North Derbyshire," p. 127.

f " Note sur l'origine des gites calaminaires." Par A. Lodin. Bull.
Soe. Geol. Fr., ser. 3, vol. xix. (1891), p. 783.

X For a description of the mine see the Geol. Surv. Mem. on " North
Derbyshire," p. 156.

§ " Notes on the Metalliferous Saddles, or ore-bearing beds in the contorted
strata of the Lower Carboniferous rooks of certain parts of Derbyshire and
North Staffordshire." By Dr. Joseph J. W. Watson. The Geologist, vol. iii.
(1860), p. 357.

|| North Derbyshire Memoir, p. 157.

jii.^cJiKAX,-) ur UIWIBERLANI), ETC. 143

in the lower. The copper-ore was chiefly chalcopyrite, associated.
however, with erubescite, and with such alteration-products as
malachite. Calcite formed the ordinary vein-stuff, but barytes
and fluorspar also occurred in the deposits.

Occasionally a pipe, incompletely filled with ore, would have
the walls of the cavity studded with fine crystals of calcite. Some
of these were large scalenohedra, enveloping crystals of copper-
pyrites, which could be seen through the translucent body of the
crystal. Such a specimen is shown here (No. 1028), and some
larger examples will be found in the Wall-case 28. Xo. 1029 is a
specimen showing barytes, or cawk, in opaque white globular
aggregates on colourless cubes of fluor. Other specimens exemplify
the forms assumed at Ecton by crystals of galena (Xo. 1023) and of
copper- pyrites (Xos. 1024, 1025).

DIVISION 2.

MINERALS OF WEST CUMBERLAND AND NORTH

LANCASHIRE.

Hematite Deposits.

(Nos. 1031 to 1008.)

The haematite deposits of North Lancashire and West Cumber-
land have so much in common that, notwithstanding their topo-
graphical severance, they may be conveniently studied together.

In West Cumberland the ore-deposits are in the Carboniferous
Limestone series of Cleator Moor and its neighbourhood ; whilst
in North Lancashire the ore-field lies north of Morecambe Bay, in
the district of Furness. Taking their names from neighbouring
towns, the former is sometimes known as the Whitehaven district
and the latter as the Ulverstone district.

These haematite deposits rank among the most important and
most interesting ore-bodies in Britain — important industrially
in consequence of the large quantity and high value of the ore ;
whilst they are interesting scientifically in that they yield a great
variety of minerals, and these of exceptional beauty.

From the discovery of stone celts in certain old workings in Fur-
ness, it has been conjectured that the ore must have attracted
attention in prehistoric times, perhaps for use as a pigment. Be
this as it may, it is probable that the ore was not neglected by the
Romans. The earliest documentary evidence with regard to haema-
tite mining in Cumberland goes back to the twelfth century, and
since that time the industry appears to have been carried on more
or less continuously. But the great development of haematite
mining was due to the introduction of the Bessemer process, soon

144 MINERALS OF WEST CUMBERLAND.

after the middle of the nineteenth century, when the ore, by reason
of its freedom from phosphorus, came to occupy a supreme position
as a material for the production of pig-iron suitable for conversion
into Bessemer steel.

According to official statistics, Cumberland furnished during 1902
as much as 1,086,391 tons of iron-ore, with an average of 52 pet
cent, of metal, valued at £787,633 ; whilst North Lancashire yielded
during the same year 482,884 tons of ore, averaging 50 per cent,
of iron, and valued at £281,682.

Hcematite, etc. (Nos. 1031 to 1046).

The character of the ordinary H&matite or red iron-ore is illustrated
by such a specimen as No. 1031. It is a hard massive mineral sub-
stance, of a bluish-purple colour. Such ore may contain cavities in
which the haematite will take the form of botryoidal or reniform
masses, known as kidney ore, as exemplified by Nos. 1032 and 1033.
Larger specimens of similar character will be found in the Wall-case
48 ; whilst some exceptionally large masses are exposed on a pedestal
between the Wall-cases 51 and 52. Certain pieces of this massive
ore present the appearance of having been hammered or beaten
on the surface. The mineral, though dark-coloured in mass, gives
a reddish-brown powder when scratched, justifying its name*
The surface may in some cases be very lustrous, and almost black,
the colour being probably due to superficial alteration to limonite.
On fracture, the reniform masses display a fibro-radiate structure,
beautifully shown by No. 1033 ; and in some cases a concentric
structure is also exhibited, the material having been deposited in
concentric zones, so that it tends to break in successive shells,
with smooth curved surfaces, as in Nos. 1035, 1036. The constituent
fibres in some cases attain a length of several inches. Some fine
examples of the perfectly conoidal fracture which the mineral
often presents are seen in No. 1034. The hard ore with conical
fracture is known locally as pencil ore. Such ore is usually
very closely grained or compact, and in consequence of its hardness
is much valued as a burnisher. Examples of haematite burnishers
as used by book-binders for giving lustre to the gilt edges of books
will be found in the case of abrasive materials in the Hall, on the
east side of the entrance to the Museum. The hard ore, being
employed for smelting, is known also as ' blast ore.'

Whilst much of the compact haematite is of this hard nature,
other kinds occur which are extremely soft. This is notably the
case in Furness (No. 1037). A specimen of soft greasy red ore, form-
ing the substance known as ruddle, is shown in No 1038. As the soft
ore is used for lining the hearths of puddling furnaces it is sometimes

* Hematite, literally « bloodstone,' from a'ifia (haima) " blood ; " the streak
giving the colour of dried blood. This mineral is to be distinguished from
the ornamental stone called by jewellers 'bloodstone,' which is a dark green
red -spotted chalcedony.

HEMATITE. 145

termed puddle ore. Some of this is of dark colour, containing
more or less manganese. The " black muck " of Ulverstone is a
dark brown substance, consisting of the oxides of iron and manganese,
with, much silica.

Deposits of haematite in limestone are very irregular in shape,
in magnitude, and in distribution ; but it is notable that they
generally occur in the neighbourhood of faults. Mr. J. D. Kendall
has classified the deposits, so far as shape is concerned, into those
which are bed-like, veia-like, and dish-like. In many cases the ore-
bearing limestone is covered with glacial drift, or boulder-clay ;
and in order to discover the irregular deposits of ore, explorers
are in the habit of probing the ground with iron-shod rods, the
presence of a deposit of haematite being indicated by a red mark
which appears at the end of the rod whenever ore is struck.

Many and varied are the views which have been advanced from
time to time in order to explain the origin of the haematite and its
distribution. Some authorities have seen in this ore evidence of
direct volcanic- activity; others have regarded it as a secondary
formation, deposited in caverns or washed into fissures in the
limestone ; whilst others again have viewed the haematite as the
result of the dehydration of pre-existing bodies of limonite, or
brown iron-ore. Possibly these views are not mutually exclusive.
The origin of the ore-deposit is one thing ; the origin of the ore
itself another, and in a general view of the whole subject there may
be room for several hypotheses.

Much evidence has accumulated in recent years tending to show
that ore-deposits such as those of Cumberland and Lancashire have
been formed in most cases by the substitution of some iron compound
for the original limestone. The ore has gradually replaced the
rock.* It is not that the haematite has generally been carried into
pre-existing fissures and caverns in the limestone — though this may
sometimes have occurred, but the rock itself has suffered a meta-
somatic change, whereby the carbonate of calcium in the neighbour-
hood of certain fissures has been replaced molecularly by iron-oxide.
Those who have made a special study of the deposits, like Mr. J. D.
Kendall and Mr. J. G. Goodchild, take this view ; but with regard
to the exact way in which the substitution was effected there is
much divergence of opinion. Probably the change was not only
very slow but indirect.

Mr. Kendall has argued in favour of the iron having been intro-
duced by volcanic activity as ferric chloride. + The reaction of
this body with the limestone might form calcium chloride and ferric
oxide, with liberation of carbonic acid ; and, given an elevated
temperature, the oxide of iron might be formed in the anhydrous

* See, for instance, " Genesis of Iron-ores by Isomorphous and Pseudo-
morphous Replacement of Limestone, etc." By James P. Kimball. Am.
Jour. 8c, [3] vol. xlii (1891), p. 231.

t " The Iron-ores of Great Britain and Ireland." By J. D. Kendall
(1893), p. 303.

14R MINERALS OF WEST C

condition. Mr. Goodchild regards it as more likely that the iron
was introduced from the red rocks which probably at one time
covered the limestone,* and in this view he is supported by many
geologists, who claim a similar origin for certain deposits of iron-ore
elsewhere.

The Carboniferous rocks of the haematite districts were probably
at one time overlain by a mantle of Permian and Triassic strata.
Meteoric waters charged with carbonic acid, filtering through the
red strata would dissolve the iron, and, in the presence of reduc-
ing agents, might carry it off in a ferrous state. When such a
solution percolated through the underlying limestone, a reaction
might be set up, whereby ferrous carbonate would take the
place of calcium carbonate. The unstable iron carbonate might
ultimately form, under oxidising influences, ferric oxide. The
anhydrous condition of the native oxide offers a difficulty, inasmuch
as water would play its part in this reaction, and the dehydration
of ferric hydrate at normal temperatures is not readily effected ;
but Mr. Groodchild has suggested that the introduction of the
haematite was probably connected with the volcanic activity which
prevailed in the north-eastern parts of the British area in early
Tertiary times. The formation of the anhydrous oxide seems to
require in most cases a moderately elevated temperature.

In support of the metasomatic origin of the haematite, Mr. Kendall
has pointed to the fact that the ore passes in many cases by insensible
gradations into the neighbouring limestone ; or, as the miners
phrase it, the ore and the rock have " grown together." Some
of the ore presents exactly the appearance of the adjacent rock
stained red, the haematite being stratified and jointed, like the
limestone, and having the same dip. Moreover, there are in the
body of the ore certain partings and nests of shale, which must
have been present in the pre-existing rock, the shaly partings in
some cases running through the ore in such a way as to prove that
they must have been in their present position before the ore was
formed.

But probably the most conclusive evidence of replacement is
found in the pseudomorphs and fossils of the haematite. The
specimen No. 1043, from the Parkside Mines, near Frizington,
shows a group of scalenohedral crystals originally of calcite, but
now composed of haematite. Here the subtle molecular change
has been effected without disturbance of external form, so that
the red iron-ore has taken the exact shape of the pre-existing dog-
tooth spar. The cavernous texture of the pseudomorph suggests
that the alteration was accompanied by a shrinkage of volume.

Occasionally, too, fossils are found in the haematite. The hard
structures of corals, crinoids, brachiopods, and certain mollusca,

£ ___

* " Contribution towards a List of the Minerals occurring in Cumberland
and Westmoreland." Trans. Cumberland Assoc, Part VII. (1882), p. 116;
" Some Observations upon the Mode of Occurrence and the Genesis of Metalli-
ferous Deposits." Proc. Geol. Assoc, vol. xi. (1889), p. 62.

147

have been found either mineralised in haematite or represented by
casts in the ore. No. 1044 shows a crinoid stem, in which the
calcareous matter has been replaced by haematite, with perfect
retention of the original form.

If such replacement can be proved to have taken place in the
case of a crystal or of a fossil, there is no difficulty in extending
the phenomenon, and conceiving that it may have been carried
out on a large scale in certain rock-masses. In limestone districts
it has often been observed that the rock in the neighbourhood of
an ore-deposit is more or less majmesian ; and this has led to the
view that partial dolomiti ation of the limestone may be the first
step towards the formationsof the ore.

Whilst admitting that most of the haematite in the North of
England has probably been formed by the chemical alteration of
limestone, it need not be denied that in some cases the mineral may
have been formed by chemical precipitation, or even by mechanical
deposition in free cavities in the rock. If the dissolution of the
limestone by acidulated waters proceeded at a greater rate than the
introduction of the ferruginous matter, open spaces would be left, and
these might become receptacles for secondary deposits of iron-ore.
Mr. J. L. Shaw holds that the haematite has in certain cases been
deposited in caverns.*

The specimen No. 1042, from Ulverstone, is an example of haema-
tite occurring as a pseudomorph after crystals of barytes, of the
characteristic crested habit. Here the formation of the haematite
must obviously have been subsequent to that of the barytes. It may
be noted that C. Doelter found haematite to be soluble in distilled
water at 80° C, and to be re-deposited in crystals. f

In the ordinary massive haematite of Cumberland there are occa-
sional cavities called loughs, and on the walls of these hollows the
ferric oxide is sometimes found crystallised in the brilliant form
of Specular iron-ore or iron-glance. A small suite of specimens,
Nos. 1039 to 1041, shows this mineral in dark steel-grey or black
lustrous crystals, of tabular or lenticular habit, associated with
finely crystallised quartz — an association often observed with
specular iron-ore elsewhere.

HaBmatite is sometimes slightly magnetic, and this is probably
due to admixture with a little magnetite, produced perhaps by
deoxidation of the ferric oxide. Magnetic iron-ore, however, is
never found in definite form in the ores of Cumberland and Lanca-
shire.

The native sesquioxide of iron suffers hydration, and thus
forms several hydrates. Turgite, or hydro-hcematite, is the name
given to a hydrate having a red streak ; whilst Goihite and limonite,
are ferric hydrates with a brown streak. The specimen No. 1045

* " The Haematite Ores of Cumberland." By James Leslie Shaw. Trans.
Fed. Inst. Min. Eng., voL iii. (1892), p. 580.
f Min. MiU, Bd. xi. (1890), p. 324.

148 MINERALS OF WEST CU..

from Ulverstone, is an example of the variety of gothite called
Lepidocrocite — a name denoting the fibro-scaly structure frequently
presented by this mineral.

Quartz (Nos. 1047 to 1054).

Silica is widely diffused through the haematite of Cumberland
and Lancashire. The massive ore contains vacuities, varying in
size from microscopic pores to cavities of considerable capacity.
In the kidney-ore the minute pores when present are usually empty,
or nearly so ; but in the common kinds of compact ore the
pores, usually very numerous, are filled to a greater or less extent
with quartz. In this way the haematite becomes a siliceous ore,
the silica shown on analysis being due to this minutely disseminated
quartz. The more siliceous the ore, as Mr. Kendal remarks, the
more numerous are these quartz-filled vacuoles. It is as though
the whole body of the ore had been suffused at some period with a
siliceous solution, probably in a heated state, and that the liquid
had deposited the silica in the pores of the mineral-mass.

In addition to these minute vacuities the haematite frequently
presents cavities, or " loughs," which may reach a considerable
size, some measuring as much as a yard across. The walls of these
cavities are, in many cases, studded with crystals of quartz and other
minerals for which the haematite mines have become famous. It
is by robbing these cavities of their sparry garniture that we obtain
those beautiful crystals which adorn all our collections, and to
which the remainder of this Case is devoted.

The suite of specimens, Nos. 1047 to 1054, illustrates the char-
acteristic features of the Quartz yielded by the haematite deposits.
The crystals are usually hexagonal pyramids, or where fully
developed bi-pyramids, the planes of the prism being generally
subordinate. No. 1048 shows bold pyramids measuring 2 ins. along
the polar edges. Much of the mineral is of a brown colour, forming
smoky quartz, and the brown tint is in some cases so deep that the
mineral appears black by reflected light, though the thinner parts
near the edges of the crystal are brown by transmitted light. The
colour of smoky quartz may usually be expelled by heating, and
is referred to the presence of an organic pigment, perhaps, according
to Forster, a compound of carbon and nitrogen, but more probably
a hydrocarbon, as pointed out by Kraatz-Koschlau and Lothar
Wohler.* The presence of titanium, as sesquioxide, in a state of
solid solution in the smoky quartz, has also been suggested by
E. Weinschenk.f

In many cases the quartz during its crystallisation has mechani-
cally entangled some of the iron-ore, and has thus become turbid
and tinted. Several specimens illustrate this formation of iron
quartz (Nos. 1051 to 1054) ; and in No. 1054 the crystals present a
brilliant scarlet colour due to inclusion of finely divided haematite.

* Min. Mit., vol. xviii. (1899), p. 326.

t Journ. Chem. Soc, vol. lxx., part ii. (1896), p. 654.

1/AIAllt. 14!)

Calcite, etc. (Xos. 1055 to 1078).

Few British minerals surpass in beauty the crystals of calcite
which have been yielded abundantly in recent years by the haematite
mines of Cumberland and North Lancashire. A large series of
these specimens is here exhibited, whilst others will be found in
•Section J of the central Horse-shoe Case, and a few of exceptional
size in a glass case opposite Wall-case 34.

Some remarkable discoveries of calcite crystals were made in
18*8 in the neighbourhood of Egremont, and described by Professor
Miers.* The collection includes a considerable number of speci-
mens from this locality, with others from the Furness district.
Many of the crystals are colourless pellucid six-sided prisms, ter-
minated by the rhombohedron (Xos. 1056 to 1058) ; other clear
crystals are acute scalenohedra (Xos. 1060 to 1062), whilst others
again are complex or highly modified crystals. The most interesting
are the twin-crystals, which have been fully described by Miers,
who has figured some of the principal types. f Some assume the
habit of the famous butterfly-twins and heart-shaped doublets
of Eyam, in Derbyshire (see No. 917, p. 132), which were discovered
many years ago, and are now extremely rare ; but the Cumberland
specimens, as seen in Xos. 1063 to 1066, are in many cases much
larger and more transparent than those from Derbyshire.

Many of the calcite crystals, from their association with the red-
iron-ore, aye more or less tinted, or even deeply coloured, with oxide
of iron (Xos. 1062, 1072) ; thus the crystals from the Stank Mine,
in Lancashire, are in many cases very effectively tinted. In
some cases a yellowish-brown ochreous substance has been mechani-
cally entangled in the crystals, thus producing more or less opacity ;
and it is noteworthy that the inclusions are in certain cases locally
distributed, so that - part only of the crystal will be opaque and
brown, whilst the rest remains limpid and colourless, as seen in
Xos. 1068 to 1070.

Dolomite, or lime-magnesia carbonate, a mineral not uncommon
in the iron-bearing limestones, is represented by the series of
specimens Xos. 1073 to 1078. These show the mineral in rhom-
bohedral crystals, with curved faces, associated with specular iron-
ore and quartz. The pearl-spar, so called from its nacreous lustre,
usually displays a superficial brown colour, due to the presence of
iron, and is often iridescent, as illustrated by several of these
specimens.

Aragonite (Xos. 107'J to 1083).

Since the haematite deposits of Cumberland and Lancashire
occur in limestone, it is by no means surprising that they should
be freely associated with carbonate of lime, but what is rather note-
worthy is the fact that this crystallised carbonate occurs not

* " Calcites from the neighbourhood of Egremont, Cumberland." Jim.
Mag. vol viii. (1889), p. 149.
f " Mineralogy," pp. 395, 397.

150 MINERALS OF WEST Ct/JMBJSKLAND.

only in the usual form of calcite but also in the less stable
form of Aragonite. The finest British aragonites occur with the
haematite of Cleator Moor. A series of typical specimens is here
exhibited (1079 to 1083), and some larger examples will be found
in Section K of the Horse-shoe Case.

Very characteristic are the long slender crystals of aragonite,
showing acute pyramids belonging to the orthorhombic system.
These spire-like crystals are often aggregated in radiating groups,
which diverge from the matrix. The mineral is very brittle, and
the sharp points of the tapering crystals are often broken off, so
that they present a premorse aspect. The cross fracture is sub-
conchoidal, and the lustre of the broken summit inclines decidedly
to a resinous aspect, whilst the remainder of the crystal exhibits
on its faces a glassy lustre.

It was shown many years ago by the experiments of Gustav
Rose — and his results have been confirmed and extended by later
observers — that aragonite may be deposited from solution of calcium
carbonate at high temperatures, whilst calcite is deposited from
cold solutions. In the haematite districts the two species occur
together, and experiment has proved that although calcite alone
is precipitated at low temperatures, both aragonite and calcite may
be deposited from warm solutions, though the aragonite pre-
dominates. Warm calcareous solutions might readily circulate
through the limestone if, as Mr. J. G. Goodchild has plausibly
conjectured, the hasmatite deposits were formed in connection with
the volcanic activity of the Tertiary period.

According to Dr. H. Credner, the character of the precipitated
carbonate of lime is partly controlled by the degree of concentra-
tion of the solution. From a pure cold solution, saturated or
moderately strong, it is thrown down as rhombohedra of calcite ;
but if the solution be more dilute it may be precipitated as
prismatic aragonite. *

It should also be noted that the character of the calcareous
deposit may be determined by the presence of foreign matter in
the solution from which precipitation occurs : thus aragonite
may be thrown down from solutions containing with the calcium
carbonate more or less sulphate of calcium or certain salts of stron-
tium, barium, or lead.

The student may find it convenient to contrast the characters
of the two species of dimorphous carbonate of lime : —

Calcite. Aragonite.

Rhombohedral system. Orthorhombic system.

Spec. grav. 2 - 7 Spec. grav. 2 - 9.

Hardness, 3. Hardness, 3 - 5 to 4.

Deposited from cold solutions, Deposited from warm solutions,

or from solutions containing or from solutions containing

alkaline silicates. gypsum, strontianite, etc.f

* Neues Jahrb., 1871, p. 288.

f "ChemischeMineralogie." Von Dr. Reinhard Brauns. Leipzig: 1896, p. 156.

BARYTES. 151

Barytes, etc. (Nos. 1084 to 1095).

Fine crystals of Barytes, or sulphate of barium, are not infre-
quently associated with the ore deposits of the Northern haematite
districts, and numerous excellent examples have been yielded by
the extensive mining operations of recent years. A rather large
series of typical specimens of barytes is here exhibited ; and the
visitor seeking further acquaintance with the mineral may study
the fine specimens in Section C of the Horse-shoe Case ; nor should
he overlook the noble crystals in the lower part of the glass case
which stands opposite to Wall-case 34.

Most of the crystals are of tabular habit, but their aggregation
gives rise to varied and in some cases quite picturesque groups,
as in Nos. 1088, 1089. By development along certain axes the
crystals become elongated, like those in No. 1087. Great diversity
of colour is exhibited by this species : whilst some crystals
are colourless (No. 1084), others are of a delicate blue tint, sug-
gestive of celestine (Nos. 1085, 1086) ; certain specimens are of
sea-gTeen colour (1092), others brownish-green (1094) or brownish-
yellow (1089) ; and in others again the brown colour becomes
deepened.

A zonal structure is seen in such crystals as Nos. 1089 and 1094.
The mode in which the mineral grows by accretion of matter from
without is strikingly illustrated by the " Phantom Crystals,"
1093 and 1094. Here the process of development of the crystal
must have been arrested for a while ; and after this pause fresh
matter was deposited, so that the nucleus became invested by a
secondary growth, whilst some slight difference in the character of
the successive deposits enables the stages of development to be
recognised.

A few other minerals from the haematite deposits are placed at
the end of the series. These include some examples of iron pyrites
(Nos. 1096, 1097), remarkably attractive by the brilliant irides-
cence of the surface. The specimen No. 1098, from Lindel-in-Furness,
is a pseudomorph of dark-coloured haematite after some cubic
species. It has been suggested that this was pyrite, and the con-
version of pyrite into haematite has been recorded from many locali-
ties. Such pseudomorphs have been described, for example, from
Torquay by Mr. R. H. Solly and Dr. A. Hutchinson.* But such
alteration is by no means common, and it seems more likely that
the original cubic mineral in the Lancashire specimen was fluorspar,
as described by Professor Miers in similar pseudomorphs from the
Stank Mine and from Dalton-in-Furness.f

* " Pseudomorphs of Haematite after Iron Pyrites." Min. Mag., vol. viii.
(1889), p. 183.

t " On some British Pseudomorphs." Ibid., vol. ix. (1897), p. 269.

1~>2 MINERALS OP CUMB

CASE IX.

DIVISION 1.
MINERALS OF CUMBERLAND.

MINERALS OF THE CALDBECK PELLS AND THE LAKE DISTRICT.

(Nos. 1099 to 1166.)

By far the larger part of this section of Case IX. is occupied by
a series of minerals from the neighbourhood of the Caldbeck Fells,
a wild district to the south-east of Wigton, in the northern part
of Cumberland. Numerous mineral- veins in this district long ago
tempted exploration, for sake of their ores of lead and copper. At
the present time, however, there are no workings in this locality.

The minerals here exhibited range themselves in two groups.
One group rather recalls the minerals of the Cornish tin-lodes, for
although the veins of quartz seem to be destitute of tinstone they
yield wolfram, scheelite, molybdenite, mispickel, apatite, and certain
minerals of bismuth. Such an assemblage at once suggests genetic
relations with an eruptive magma, like that of the neighbouring
granitic rocks.* The minerals may have been introduced into the
veins from plutonic sources, while the magma was in a highly heated
condition. Although the minerals are rather vaguely referred in
most collections to the Caldbeck Fells area, Mr. Goodchild has
pointed out that the precise locality which has yielded most of
them is the neighbourhood of Brandy Gill, where the rocks are
traversed by parallel veins running in a north and south direction.

The second group is formed by the lead-and copper-ores of Cald-
beck Fells, which appear to be of later date than the minerals just
indicated. These ores come chiefly from Red Gill and Roughten
Gill, or, as it is sometimes spelt, Rowtin Gill. Galena, blende,
and chalcopyrite seem, as usual, to have been the original minerals,
but near the outcrop of the veins they have given rise to a number
of secondary products, including minerals of great beauty, like
linarite. Mr. Goodchild has argued, with much plausibility, in
favour of the view that the later infilling of the veins was due to
the thermal waters brought up during the great volcanic outbursts
of Tertiary times, or immediately subsequent thereto.f Apart

* For the igneous rooks of th? district see Mr. Alfred Harker's papers in
Quart. Journ. Geol. Soc. vol. 1. (1894), p. 311 ; vol. li. (1895), pp. 125, 139.

"j" '" Some Observations upon the Mode of Occurrence and the Genesis of
Metalliferous Deposits." Proc. Geol. Assoc, vol. xi. (1889), p. 45.

APATITE AND WOLFRAM. 153

from direct outflows, the formation of a vast system of dykes suffi-
ciently demonstrates, as Sir A. Geikie has forcibly shown, how
intense and widespread must have been the subterranean activity
in the northern part of the British area during the Tertiary period.*
W aters laden with mineral matter would travel along the heated
highways opened up by the Assuring of the rocks, and deposition
might occur on reduction of temperature and diminution of pressure,
so that the latest phases of vulcanicity would probably represent
the most favourable conditions for mineral precipitation in the
veins. Mr. Harker has suggested, though with due reserve, that
the gabbro and granite of Carrock Fell may be of Tertiary age.f

Apatite (Xos. 1099 to 1104).

Xo part of Britain, with the exception of Devonshire, has yielded
finer crystals of Apatite than those which have occasionally been
found in the quartz-veins at the foot of Brandy Gill. A suite of
fine specimens is here exhibited, showing the mineral in prismatic
crystals striated longitudinally and terminated by the basal pina-
coid.? L Some specimens, like Xo. 1100, are of a beautiful blue colour,
like typical beryl ; others are of a celadon-green tint (Xo. 1099),
whilst others again are not uniformly coloured, but the pale green
passes at one extremity into a delicate pink, rather like the well-
known parti-coloured tourmalines (Xos. 1101, 1102). The apatite
is associated, in the quartz matrix, with gilbertite (Nos. 1099 to
1103), and in one specimen (No. 1104) is accompanied by wolfram —
an association rather suggestive of that occurring in Cornwall. Xo
analysis of the Cumberland apatite seems to have been recorded.

Wolfram and Scheelite (Nos. 1105 to 1111).

In connection with the Cornish tin-lodes, Wolfram or ivolframite
has already been described (p. 30). It is one of a small group of
minerals crystallizing in the monoclinic system. There is a rare
species called Ferberite, which is essentially a tungstate of iron,
and another called Hubnerite, essentially a tungstate of manganese,
but in Wolfram the two compounds occur as an isomorphous
mixture, so that the ratio of the two metals, iron and manganese,
is subject to variation.

No. 1108 is a specimen of wolfram ochre or tungstic ochre, known
as tungstite, which is a trioxide of tungsten, formed by the alteration
of wolfram. In several of the specimens, as Nos. 1109 and 1110,
the wolfram is seen in association with Scheelite. This mineral occurs
in Cumberland well crystallised in tetragonal bi-pyramids, as illus-
trated by Nos. 1110 and 1111, where the bold crystals exhibit the
characteristic brownish-yellow colour, associated with a lustre almost
adamantine. This species, named after the Swedish chemist Scheele,
who first detected tungsten, is a tungstate of calcium. Although

* " The Ancient Volcanoes of Great Britain," vol. ii., book viii.
+ Gpo1. 8nrv. Mem., on Sfcye (1904), p. 170.

7882. M

154 MINERALS OF CUMBaiti,AJNU.

it may have originated in some cases from wolfram, the converse
change is not uncommon. Pseudomorphs of wolfram after scheelite
point to the substitution of iron and manganese for calcium. Such
change has been described, for instance, by Mr. W. H. Hobbs, as
occurring at Trumbull, Connecticut, where wolfram is mined.*
Scheelite is, in some cases, a companion of gold ores, as described
by Sir C. Foster in the Pesterana district.

Molybdenite, etc, (Nos. 1112 to 1115.)

In most scheelite molybdenum is present, to a greater or
less extent replacing the tungsten, and it is said that the darker
the colour of the scheelite the greater is generally the proportion
of molybdenum. f Between molybdenum and tungsten there is,
indeed, much relationship. Molybdenum occurs native as a di-
sulphide forming the mineral called molybdenite. Some excellent
specimens of this rather rare species are here exhibited (Nos. 1112
to 1113) showing the mineral in soft, brilliant graphite-like scales
and crystalline plates associated with wolfram and scheelite in the
quartz- veins of Brandy Gill. In No. 1114 the molybdenite is coated
with a thin, yellow incrustation of molybdite, of molybdic ochre, an
oxide evidently formed at the expense of the sulphide, on which it
is parasitic.

Molybdenite occurs in thin, metallic scales in certain granitic
and other igneous rocks. It is found, for example, in the joints
of the Shap granite,^ and in the granite of Mount Sorrel, § where ib
is known to the quarrymen as "lead."

It is interesting to note that Mr. Goodchild has recorded the
occurrence of a mineral believed to be Wulfenite, or molybdate of
lead, in one of the gills running up from the Cawda to the west side
of Carrick.ll As both molybdenite and galena occur in the veins
of this district, the conditions for the formation of such a mineral
are not far to seek.

Grunlingite {Nos. 1116 to 1118).

The two rhombohedral metals, tellurium and bismuth, occur ia
combination as telluric bismuth ; and the related elements, selenium,
and sulphur, may also be present in variable proportion. A
combination containing Bi 2 Te 2 S has been distinguished as a
definite species under the name of Tetradymite. Suph a mineral
occurs with the gold ores of North Wales (p. 130), and it has long

* Twenty-second Annual Report U.S, Geol. Surv., Part ii., 1901.

f H. Traube in Neues Jahr. Beilage Bd. vii. (1890), p. 232. The Cumberland
Scheelite contains 0-35 per cent, of Mo0 3 .

\ " The Shap Granite." By Alfred Harker and J. E. Marr. Quart. Journ.
Geol. Soc, vol. xlvii. (1891), p. 266.

§ " On the Occurrence of Molybdenite in Leicestershire." By Dr. C. Le Neve
Foster, Geol. Mag., vol. iii. (1866), p. 523.

|| " Wulfenite at Caldbeck Fell." Geol Mag. [N.S.], Dec. % vol. ii. (1875),
jj. 565. ' \ ■ <

PYROMORPHITE. 155

been known that a similar mineral is occasionally found in the
quartz-veins of Brandy Gill. An allied mineral from Brazil has
been called Juseite. The Cumberland mineral was examined long
ago by Rammelsberg, but fresh analyses were made a few
years back by W. Muthmann and E. Schroder, in Munich. They
found that it contained about 12 per cent, of tellurium, leading
to the formula Bi 4 S : Te, and as this differs markedly from the
formula of true tetradymite they regarded the Cumberland
mineral as a new species, for which they proposed the name
Griinlingite, in compliment to Dr. J. Griinling, the Curator of the
Mineral Collection in Munich.* The mineral occurs in cleavable
laminar masses, with brilliant metallic lustre, and from certain
measurements made in Dr. Gmth's laboratory by Mr. Herbert
t>mith, the mineral seems to agree with tetradymite in its system
of crystallisation.

Pyromorphite, etc. (Nos. 1119 to 1138).

Among the minerals yielded by the lead-lodes of the Caldbeck
Fells, some of the finest are specimens of Pyromorphite, formerly
obtained from shallow workings at Roughten Gill. The rather
extensive series of specimens, Nos. 1119 to 1130, will seive to illus-
trate the varieties presented locally by this species. Most of the
specimens show the pyromorphite in crystals of prismatic habit,
the hexagonal prisms being in some cases slightly hollow or cavern-
ous. The mineral is called green ore or brown ore, according to its
colour, but some of the finest crystals are of greenish yellow tints.
However deep the colour, the streak of the mineral is nearly white.
White pyromorphite, like No. 1130, generally contains calcium,
and is regarded as an isomorphous mixture with apatite.

Pyromorphite is a chloro-phosphate of lead, which in most cases
appears to have been formed from galena. Pseudomorphs of
pyromorphite after galena are known, but curiously enough the
reverse change is also attested by pseudomorphs of galena after
pyromorphite, or " blue lead-ore," as noticed at p. 55.

The presence of apatite rather abundantly in the Caldbeck Fells
district suggests that it may be genetically connected with the
pyromorphite. Apatite is readily soluble in water containing
carbonic acid, as Professor Truchot has shown, and such a solution
reacting with cerussite derived from galena, would give rise to phos-
phate of lead. This at least is the explanation suggested by
M. Gonnard to explain the origin of the pyromorphite of
Pontgibaud.f

Associated with the pyromorphite of Roughten Gill, there occa-
sionally occurs a smalt-blue or lavender-coloured mineral, formerly

* " Ueber die Zusammensetzung einlger Tellurmineralien." ZtiU. Kryst.
u. Min., vol. xxix. (1898), p. 140 : " GrunKngit, einneues Mineral," p. 144.

t " De la genese des phosphates et arseniophosphates plombiferes de
Roure et de Roaierg (Pontgjbaud)." BvU. Soc. Min. Fr., vol. vi. (1888),
p. 35.

7882. M 2

156 MINERALS OF CUMBERLAND.

regarded as a kind of calamine, but shown by Professor Miers,
from examination by Mr. G. T. Prior, to be a phosphate of lead
and aluminium.* Specimens are seen in Nos. 1132 to 1134. Ana-
lyses by Mr. E. G. J. Hartley, in the mineralogical laboratory at
Oxford,f have proved it to be identical with a mineral from Georgia,
described many years ago by Professor Shepherd under the name
of Hitchcockite. The blue colour is probably due to the presence
of a small proportion of copper. The Cumberland hitchcockite
in some cases invests, and in others appears to replace, the pyro-
morphite, thus giving rise to pseudomorphs, as well seen in the speci-
mens here displayed.

In pyromorphite, the phosphorus may be replaced to a greater
or less extent by arsenic, and the species may thus pass gradually
into the chloro-arsenate of lead, known as Mimetite. This is generally
a yellow or brown mineral, sometimes beautifully orange-coloured,
as well shown by the finefspecimens Nos. 1135 to 1138. These
specimens came from Dry Gill, at a short distance to the east of
Roughten Gill, where the mineral occurred formerly in such abun-
dance that it was worked commercially. The crystals are aggregated
in six-sided groups, which, by their general shape, are suggestive
of miniature barrels, and the pronounced curvature of the prism
faces has earned for this variety the name of Campylite. In some
cases the curvature is so great that the mineral forms almost spheri-
cal masses. The campylite was associated, as some of the specimens
here show, with psilomelane and with barytes, well seen in No.
1135. According to Greg and Lettsom, it was worked not only as
an ore but for direct use in the manufacture of flint-glass, to which
it was reputed to impart exceptional brilliancy.J The mineral
contains a small proportion of phosphate, as is usually the case with
mimetite ; whilst conversely most pyromorphite shows traces of
the arsenate. The source of the arsenic in mimetite is probably
to be found in the mispickel, or arsenical pyrite, not uncommon
in the veins of the Caldbeck Fells district.

It is noteworthy that the two isomorphous minerals, the chloro-
phosphate and the chloro-arsenate of lead exhibit certain optical
anomalies, pyromorphite being sometimes and mimetite always
biaxial.§ Professor Miers remarks that " the pyromorphite of
Roughten Gill seems to consist in the middle of uniaxial pyro-
morphite and at the side of biaxial mimetite. Since, however,
pure mimetite is almost unknown, the biaxiality of the mineral
may be really due to strains set up by isomorphous intermixture." ^f

* " On some British Pseudomorphs." Min. Mag., vol. xi. (1897), p. 272.

+ " On the Constitution of the Natural Arsenates and Phosphates." Part iii.
" Plumbogummite and Hitchoookite," Ibid., vol. xii. (1900), p. 223. Also,
Prof. Miers's " Notes on the HitohcooHte, etc." Ibid., p. 239.
•yt" Mineralogy of Great Britain." p. 407.

F5T§ Optical anomalies are apparent irregularities in the relationship normally
subsisting between optioal oharaoters and crystalline symmetry.

«[ " Mineralogy," p. 515.

LEAD AXD COPPER ORES. 157

Cerussite, Anglesite, and Linarite (Nos. 1139 to 1146).

The oxidised ores of lead, occurring within the zone of weathering
in the deposits of Roughten Gill and Red Gill, include not only the
phosphates and arsenates, but, as might be expected, the more
common minerals in which lead appears as carbonate and sulphate.
As such minerals have been described already in connection with the
Derbyshire collection, (pp. i:>\ 139) very little need here be added.
Nos. 1139 to 1142 are examples of crystallised Cerussite, or lead
carbonate, associated in No. 1141 with malachite, whilst No.
1143 is a specimen of the less common mineral Anglesite or lead
sulphate.

Some attention, however, is demanded by the rare and beautiful
species called Linarite, of which some excellent specimens are here
shown (Nos. 1144 to 1146). This mineral was originally noticed
by Sowerby, who regarded it, pardonably enough in his day, as a
blue carbonate of copper.* It was afterwards studied chemically
and crystallographically by Mr. H. J. Brooke, with the result'that
he determined it to be a " cupreous sulphate of lead." t Brooke
conferred upon it no specific name, but it was subsequently called
Linarite, from Linares, a mining locality in the south of Spain.
The specimens studied by Sowerby and by Brooke were from
Scotland.

Linarite occurs in crystals of tabular and prismatic habit, belong-
ing to the monoclinic system, and presenting a deep azure-blue
colour, with a brilliant vitreous lustre. It is a basic sulphate of
lead and copper, and has no doubt been formed by the oxidation
of lead and copper sulphides, such as occur in the ore-deposits of
Cumberland. The late Mr. Patrick Dudgeon detected it in the
cavities in slag from old Roman lead-smelting works, in Dumfries,
where it had evidently resulted from alteration by exposure.^

The minerals Leadhillite and Caledonite have been recorded as
occurring with the linarite of Cumberland, but no specimens are
at present in the collection. (For these species, see p. 208.)

Malachite, Brochantite, etc. (Nos. 1147 to 1155).

Wherever copper-ores are subjected to meteoric influences, Mala-
chite is likely to be formed, and by its colour to assert its presence.
In the ore-deposits of Caldbeck Fells, the copper-pyrites, by altera-
tion, has yielded this conspicuous mineral in many localities ; and
some fair specimens are here exhibited (Nos. 1147 to 1150). The
mineral is a basic cupric carbonate, appearing generally in acicular
crystals, or in fibrous masses and incrustations, of bright green
or sometimes very dark green colour. In Nos. 1149 and 1150,
from Braithwaite, it is associated with white acicular crystals of
cerussite, showing that superficial agencies acting on mixed ores

* " British Mineralogy," vol. iii. (1809), p. 5.

t " On a New Lead Ore." Ann. Phil., new ser., vol. iv., (1822) p. 117.

% Min. Mag., vol. v. (1884), p. 33.

153 VUNERALS OP CUili

^HXVJ-J^l-Lt XJi

of copper and lead have brought both metals into the state of car-
bonates. Azurite, or blue carbonate of copper, though occurring
in the Caldbeck Fells area, is a rarer mineral than the green carbonate
and does not happen to be represented in this collection.

Several examples of the basic sulphate of copper called Brochantite
are here exhibited (Nos. 1151 to 1153). At Roughten Gill this rare
mineral occasionally occurs in small crystals of dark green colour,
associated with malachite and chrysocolla. Mr. W. Semmons has
insisted on the frequent relationship of the sulphates and silicates
of copper.* Pseudomorphs of chrysocolla after brochantite are
known.

A specimen of Chrysocolla, or hydrated basic silicate of copper,
from Roughten Gill, shows the mineral in the form of small globular
masses of bluish-green colour, on a quartzose veinstone (No. 1154).

Rarer than most of the other copper-bearing minerals in this
Case is the species termed Aurichalcite, of which a beautiful specimen
from Roughten Gill is here exhibited (No. 1155). This is evidently
a secondary mineral due to the weathering of mixed ores of zinc
and copper, since it consists of a basic carbonate of both metals.
In consequence of its containing the constituent metals of brass,
it was called by the early mineralogists brass-ore, or an equivalent
name. The aurichalcite here shown occurs in fibres or minute
acicular crystals, of a delicate turquoise blue tint, investing quartz.
Another Cumberland specimen (No. 1206), will be found in the oppo-
site side of the Case, among the minerals of Alston Moor.

Hemimorphite (Nos. 1156 to 1161).

The eye of the visitor will be attracted by the beautiful sky-blue
colour of the mammillary deposits of this species, as exhibited in
the specimens from Roughten Gill. The deposits are laminated and
consist of acicular crystals, which owe their colour, it is believed,
to the presence of copper, whence the mineral has been' called
cupreous calamine.

Mention has already been made (p. 109) of the confusion in
nomenclature with regard to the oxidised minerals of zinc. The
term Calamine, restricted in this work to the carbonate, is often
applied to the silicate, whilst the term Smithsonite is used by some
authorities to designate the silicate and by others to denote the
carbonate. Calamine is a word much too venerable to be displaced,
but in order to avoid ambiguity with regard to the smithsonite,
it seems well to abolish its use altogether, and to distinguish the
hydrous silicate by the term Hemimorphite, which was introduced
by Kenngott in 1853. The anhydrous silicate, known as WiUemite,
is not recorded among British zinc-ores.

Hemimorphite is commonly described as a hydrated zinc silicate,
but since it has been shown that it requires exposure to a red heat
before the water is expelled, the mineral may be rather regarded

* " On Brochantite and its Associations." Min. Mag., vol. iv. (1882),
p. 259.

GRAPHITE, ETC. l"/t

as a basic silicate. It crystallises in the orthorhombic system,
and the term hemimorphite has reference to the hemimorphic
characters of its crystals, that is to say, the opposite ends are crystal -
1 Graphically dissimilar. Most hemimorphic crystals are pyro-
electric, or become electric when heated, whence hemimorphite
is often called electric calamine. That end of a crystal which becomes
positively charged as the temperature rises is termed the analogous
pole, whilst the opposite end, becoming negative, is called the antil og-
ous pole. On cooling, the character of the electricity is reversed.
The phenomenon is well illustrated by Kundt's method, as applied
by Professor Miers, which consists in dusting over the electrified
crystal a fine mixture of red lead and sulphur, rendered electric
by shaking, when the sulphur adheres to the part which is positively
charged and the red lead to the negatively electrified portion.

Zinc silicates may be formed naturally by the reaction of alkaline
silicates on sulphate of zinc, resulting from the oxidation of blende.
The Cumberland hemimorphite exhibits mammillated forms sugges-
tive of deposition from solution, in the manner of stalagmitdc
growths.

Tourmaline, Garnet, etc. (Nos. 1162 to 116.5).

Following the silicate of zinc are a few specimens of other silicates
from Cumberland. No. 1162 is an example of Tourmaline, from the
Caldbeck Fells district, showing the mineral in brown, radiating
fibres on quartz.

No. 1163 is a specimen of Epidote, from Willow Craig near Keswick ;
No. 1164: an example of Garnet in well-defined crystals from Derwent-
water;* and No. 1165 a piece of Skiddaw slate, enclosing character-
istic crystals of Chiastolite, a variety of andalusite, well known as a
product of contact-metamorphism. In the Petrological Collection
there is a large series of rock-specimens from the Lake District of
Cumberland and Westmorland, and the visitor may be referred to
that Collection for better examples of the various crystallised silicates
from the igneous and metamorphic rocks.

Graphite (Xo. 1166).
In parts of the Lake District there are certain veins of copper
and lead-ores, whilst minerals containing antimony, nickel, and
cobalt have also been recorded. The Keswick copper-mines were
formerly of great reputation, and a description — both geological
and historical — will be found in the Geological Survey Memoir by
the late Mr. Clifton Ward.f But the most interesting mineral of
Lakeland is undoubtedly the well-known Graphite or Plumbago,
commonly called black lead — the material of the famous Cumberland
pencils. In old documents the mineral is referred to under the
name of wad — a name now generally restricted to certain oxides of

* The garnet-bearing rocks of Lakeland were studied by the late Mr. E. E.
Walker. Quart. Journ. Oeol. Soc., vol. lx. (1904), p. 70.

+ "The Geology of the Northern Part of the English Lake District."
Stem/ Oeol. Burv., 1876.

i60 MINERALS OF CUMBE

manganese — and it is also termed black cawk — the term " cawk '
being elsewhere applied only to barytes. Only one specimen o
Cumberland graphite is shown here (No. 1166), but a rather exten
sive series of examples will b« found in Section B of the Horse-
shoe Case and in the drawer under Section E.

The Cumberland graphite, now extremely rare, was found in pipes,
strings, and irregular masses called " sops," which occurred, according
to Mr. Ward,* in association with a dyke, or sill, of altered
diorite and with intrusive masses of diabase, in the old volcanic
series of Borrowdale. Small veins of quartz run through the diorite,
and an old writer speaks of the black-lead as being associated with
" quarts and chrystles."f

Dr. Percy held that the special value of the Borrowdale graphite
depended rather upon its peculiar physical condition, upon its state
of aggregation more than upon its chemical purity ; for, as a
matter of fact, it contains a rather considerable proportion of foreign
matter, which, on the combustion of the carbon, is left as ash, to
the extent of about 12 per cent.f

The general origin of graphite is a subject by no means free from
obscurity. In some cases there can be no doubt that graphite
represents an extreme stage of carbonisation of organic matter.
Specimens in the Horse-shoe Case, presented by J. Smith, Esq.,
illustrate the alteration of coal to graphite by the proximity of an
intrusive eruptive rock, at Craigmair, near New Cumnock, in
Ayrshire. § In certain graphitic schists the mineral occurs as dissem-
inated black dust, probably developed by contact-metamorphism.

Artificial graphite is familiar to the metallurgist, as occurring
in the form of dark lustrous scales in grey pig-iron. Molten cast
iron dissolves carbon, and when supersaturated the excess may
separate, on cooling, as crystalline graphite. Such a material i3
known to the workmen as " kish." Under conditions of great
pressure, carbon may be obtained from solution in molten metal
not only in the form of graphite, but, as M. Moissan discovered,
in the form also of diamond.

An opinion has recently been gaining ground in favour of the
origin of natural carbon, in many cases, from the decomposition
of metallic carbides, of deep-seated origin. The action of water
on such carbides would give rise to hydrocarbons, as M. Mendeleef
pointed out, in discussing the origin of petroleum. Professor
J. Walther, who has studied the occurrence of graphite in the
gneissose rocks of Ceylon, favours the view that the mineral has
there resulted from the reduction of certain volatile hydrocarbons. ||

* " The Geology of the Northern Part of the English Lake District," p. 60.
Plans and Sections of the Borrowdale Mine are given.

t " The History of the County of Cumberland." By William Hutchinson.
1794. vol. ii. p. 220.

% " Metallurgy : Fuel, etc." 1875. p. 103.

§ Trans. Geol. Soc. Glasgow, vol. x. (1896), p. 257.

|| " Ueber Graphitgange in zersetzten Gneiss (Laterit) von Ceylon." Zeitsch.
Deutsch. Geolog. Gesell. vol. xli. (1889), p. 359. See also Max Diersche in
Jehrb. d. K.-K. Geol. Beiehsanst., vol. zlriii. 1898), p. 231.

161
DIVISION 2.
MINERALS OF THE NORTHERN LEAD DISTRICTS.

ORES OF LEAD AND ZINC J BARYTES, ETC.

(Nos. 1167 to 1234.)

Deposits of lead-ore are distributed more or less abundantly
through the Carboniferous rocks of an extensive tract of country
in the North of England, comprising parts of the counties of Cum-
berland, Westmorland, Northumberland, Durham, and Yorkshire.
This vaguely defined area may perhaps be regarded as having its
centre in Alston Moor — a wild district in Cumberland, on the borders
of Westmorland, described as being almost the centre of Britain
itself. * The occurrence of the ores in the Northern Lead Districts
is similar to that of the corresponding minerals in the Carboniferous
Limestone of Derbyshire. The galena is accompanied by zinc-
blende, and the veinstufi is composed chiefly of calcite, fluor-spar
and barytes, though quartz is present in some of the ore-deposits,
especially in those which are located in or near siliceous rocks.
Some of the lead-ore, such as that formerly worked in large quantity
at Grassington in Yorkshire, is in Millstone Grit.

The Carboniferous Limestone series consists of an alternation
of limestones, sandstones, and shales, varying considerably in
thickness in different districts, but reaching a maximum of about
2,800 feet, though at Alston Moor its thickness is only about half
this aggregate. Intercalated with the Carboniferous strata is
the great sheet of intrusive rock known as the Whin-sill, which at
Alston Moor is about 120 feet thick, whilst elsewhere it may reach a
yet greater development.

The Lead measures, or ore-bearing strata, he between the Whin-
sill and the Fell Top Limestone. The Millstone Grit, which must
at one time have spread over the whole of the Carboniferous Lime-
stone series of the Pennine range, has been mostly removed by
denudation, but patches are left here and there, in some cases of
considerable extent. Most of the veins are fault-veins, and the
veinstones are much brecciated. The principal workings are, or
have been, situated near the upper waters of the South Tyne, the
Allen, the Wear, the Derwent, and the Tees.

Several types of ore-repositories are recognised in the northern
lead districts. The Rake veins known also as right-running veins,
usually take an approximately east and west course. It is observed
that they are generally more productive in hard rock, like limestone,
than in soft rock like shale. The cross-veins, running roughly north
and south, and apparently of later formation than the rakes, have
been found to carry much lead-ore when in the Great Limestone, but

* " On the Lead-mining Districts of the North of England."By T. Sopwith,
M.A., F.R.S. Trans. N. Eng. Inst. Min. Eng., voL xiii. (1864), p. 187.

162 MINERALS OP THE NORTHERN I

to yield little in the strata above ; whilst in the beds below, the lead
is not infrequently accompanied by copper-ore. A third class,
including smaller veins containing but little ore, have an inter-
mediate bearing, and are called quarter-point veins. There are
also the large ore-bodies termed flats, or flots, which are irregular
sheets or flattened pockets often roughly parallel to the stratification,
and connected by fissures, vertical or oblique, containing more or
less mineral. The cavities in the flats yield some of the finest speci-
mens of crystallised minerals, especially of calcite and fluor.

Although the Alston mines may have been worked at a very
remote period, the earliest known reference to them is contained
in a document dated a.d. 1131, in which a certain mine, identified
with some of the old Alston workings, is referred to as the " Carlisle
Silver Mine." * Some of the galena formerly worked must have
been highly argentiferous, and pieces of ore rich in silver have
occasionally been found even in recent times. Certain fragments
of '' float-ore " have yielded, according to Mr. Cameron Swan,f
as much as twelve ounces of silver to the ton of lead, though the
ore at present worked in the Alston district is by no means rich,
the average of Nenthead and of Weardale lead-ore being, according
to the same authority, only about seven or eight ounces of silver
per ton of pig-lead. It has often been remarked that galena is
less highly argentiferous in limestone than in veins running
through slates and grits.

The lead-ore of the Alston district is associated with more or less
zinc-ore, which is now extensively worked by the Vieille Montagne
Co. Though formerly zinc-blende was regarded as worthless and
practically a nuisance, it is this mineral which now forms the chief
object of exploration in the district.

Thus, according to official statistics, Cumberland yielded in 1902
as much as 7,826 tons of zinc-ore and only 1,273 tons of lead-ore
whilst Northumberland produced 3,056 tons of zinc-ore and but
600 tons of lead-ore. On the other hand there were raised in Dur-
ham 2,760 tons of lead-ore against thirty-seven tons of zinc-ore;
whilst in Westmorland and Yorkshire no zinc-ore was returned,
though the former county produced 1,424 tons of lead-ore and
the latter 662 tons.

Galena (Nos. 1167 to 1188).

Some sharply defined crystals of Galena are here exhibited from
Alston Moor, notably the large cubes, associated with pearl-spar,
in No. 1168. In the specimen No, 1169, the galena is crystallised
in cubo-octahedra, and the cube-faces are deeply corroded, exhibiting
what miners call " seals." Several specimens, such as 1173 and
1174, display an iridescence on the tarnished faces of the galena

. * " The . Alston Mines." By the Rev. W. Nail, M.A. Trans. Inst. Min.
Eng., vol. xxiv. (1903), p. 392.

l f Discussion on the foregoing paper : Remarks by W. J. Cameron Swan of
Newcastlerupon-Tyne. p. 406.

l_.Al.f-> A.

163

crystals. The lead sulphide is associated with calcite in Nos. 1172,
1174 ; with fluor-spar in Nos. 1176 to 1182 ; and with quartz in
1167. In No. 1173 the cubic crystals of galena are partly covered
with cubes of white fluor, upon which is a small crop of quartz-
crystals. No. 1188, a specimen from the Craven district in York-
shire shows the crystalline galena gradually passing towards the
surface into compact cerussite, or lead carbonate.

The origin of galena in limestone rocks has been the subject of
much discussion. It has often been suggested that the common
association of lead-ore with limestone may have some relation to
the organic nature of the rock. From the widespread occurrence
of galena in the Carboniferous Limestone, this rock has been called
by miners the " Mother of Lead." In some cases plumbiferous
solutions may have been reduced by the action of organic matter.
Thus, among the specimens in Case 37 illustrating the processes
of fossilisation will be found an example of wood mineralised with
galena.* Dr. R. W. Raymond described an iron pickaxe from an
old mine in the Cerillos range of New Mexico, in which the eye of
the axe had been filled with crystallised galena, probably formed from
the reduction of lead sulphate by the decaying wood of the pick-
handle. Allusion has already been made (p. 118), to the occurrence
of galena in coal, where the de-oxidising action of the carbonaceous
matter seems to have been responsible for the reduction of galena
from a solution of the sulphate. That the formation of galena
has not necessarily required a high temperature is clearly attested
by its occurrence in veins traversing coal-seams without altering
the adjacent coal. No. 1186 is a specimen, presented many years
ago by the Earl of Carlisle, shewing the galena associated with
coal as it occurred at Netherland in Northumberland. f

According to the late Mr. Wallace, the formation of the galena
is comparatively recent, and may be still going on in the neigh-
bourhood of Alston Moor. J In support of this view he called atten-
tion to certain small crystals of galena, known as " buttons of ore,"
which stud the walls of some of the caverns in the district and are
believed to be of quite recent formation. This observer, who
was a resident in the midst of the mines, held that the lead-ore had
been derived from the rocks of the district, through which it had
been diffused in small proportion and whence it had been removed
in solution. He remarked that those veins which were most pro-
ductive were the farthest removed from igneous rocks.

* This speoimen is from Freihung in Bavaria, and is exhibited in the Table-
case, No. 37, on the opposite side of the Museum, close to Oase No. 1 of this collec-
tion of British Minerals. The Freihung Mines, which have yielded the tree-stems
in which the tissues are partly replaced by galena, are in the Trias.

t On the reducing action of coal and other carbonaceous substances, see
Dr. W. P. Jenny, Trans. Am. Inst. Min. Eng., vol. xxxiii (1903), p. 445.

% " The Laws which regulate the Deposition of Lead -ore in Veins ; illustrated
by an examination of the geological structure of the Mining Districts' of
'Alston Moor." By William Wallace. 1861. • - • - - : ••' '

164 MINERALS OF THE NORTHERN L

Admitting that the galena may in some cases have been leached
out of the neighbouring strata and concentrated in specific ore-
repositories, the difficulty still remains as to the genesis of the
mineral in the rocks themselves, since these can be regarded only
as a proximate source of the ore. Even the migration of the lead
is not free from difficulty. The sulphide is rather a stable and
sedentary mineral, whilst the sulphate is not markedly locomotive,
and when formed by oxidation of the galena seems likely to remain
near its original location. But though the sulphate of lead is only
sparingly soluble in pure water, its solubility is increased by the
presence of carbonic acid, whilst it is freely soluble, as shown by
Doelter, in a solution of alkaline sulphide. It is possibly in the latter
condition that it circulates through certain ore-bearing rocks.

Of late years there has been a great tendency to regard deposits
of galena in limestone as having, in most cases, resulted from meta-
somatic action, that is to say, there has been molecular replacement
of the rock by the ore. This view was advanced by Mr. F. S. Em-
mons in his masterly work on the great deposits of silver-lead ore
at Leadville ; * and similar views have since been extended, with
much acuteness by other observers, to explain the formation of
galena-deposits in many other localities. Pseudomorphs showing
the replacement of calcite by galena are, however, by no means
common, but there is no doubt about the occurrence of such a change
in the case of certain fossils. Thus, the late Mr. Townshend Hall
recorded the occurrence of fossil corals mineralised with galena
in Devonian rocks between Ilfracombe and Combe Martin.f The
replacement of calcite by galena has been studied in microscopic
sections of certain ore-bearing rocks, by Mr. W. Lindgren.J

Roughly stated, it may be said that as the molecules of limestone
were removed by solution their place was taken, without formation
of spaces, by molecules of galena. Probably, however, it was not
a simple case of simultaneous removal of one substance and pre-
cipitation of another, but rather a case involving complex chemical
changes.

It has often been observed, and the observation holds true to some
extent in the Northern lead-districts, that deposits of lead and
zinc-ores are more common in limestones that are dolomitic than
in those of normal type. Dolomite readily lends itself to meta-
somatic alteration, partly perhaps in consequence of its cavernous
structure, for a free circulation of fluids through a rock is naturally
favourable to its alteration. Permeable rocks admitting of ready
percolation, or fissured rocks which offer conduits for the easy move-
ment of liquids are just the rocks that may be expected to contain
mineral matter, even though the solutions which traverse them

* " Geology and Mining Industry of Leadville, Colorado." By Samuel
Franklin Emmons. Monographs U.S. Oeol. Surv., vol. xii. (1886).

f " On the Association of Minerals and Fossils in North Devon." Trans.
Dev. Ass., vol. xxii. (1890), p, 166.

% " Metasomatic Processes in Fissure Veins." Trans. Am. Inst. Min. Eng.,
▼oL xxx (1901), p. 578.

LEAD AND ZINC ORES,

165

are but dilute. The metal-bearing solution may flow through one
channel, whilst the precipitant travels along another, and the com-
mingling of the liquids may lead to deposition of ore. Bischof ob-
tained crystals of galena by the protracted action of sulphuretted
hydrogen on a very dilute solution of a lead salt.

In the opinion of Mr. J. G. Goodchild, who has an extensive
acquaintance with the ore-deposits of Cumberland and Westmor-
land, the galena probably originated during the last upheaval of the
district, when the volcanic agencies which had been so active ir>
early Tertiary times were gradually waning, and wire represented
by numerous hot springs.* Thermal waters rising from deep sources
brought up metallic sulphides, which would be deposited when the
heat was sufficiently lessened and the pressure reduced. He con-
siders it likely that the lead-ore had originally a wide extension
through the rocks in the form of a series of shallow disconnected
deposits.

Cerussite {Nos. 1188 to 1190).

Carbonate of lead is the most common product of the alteration
of galena, but the Alston district is not remarkable for crystals of
this species. By the miner it is known as white ore, but though
containing a large proportion of metal it was regarded by the early
explorers as a sparry mineral of no value. Its formation is illus-
trated by such a specimen as No. 1188, from the Craven district
in Yorkshire, where it surrounds a nucleus of the unaltered
sulphide. Careful examination of similar specimens has sometimes
revealed a thin layer of sulphate of lead beneath the carbonate,
suggesting that the galena was first altered to sulphate and this
converted to carbonate by reaction with the limestone matrix.

Since cerussite is a secondary mineral, due to epigenic action,
it is not commonly found at great depths or in old mines. Crystals
are occasionally found seated on galena as the parent mineral.
The crystals are isomorphous with those of the carbonates of barium
and strontium, and with carbonate of calcium in the state of
aragonite.

Blende (Nos. 1191 to 1202).

The sulphide of zinc or zinc-blende, formerly despised under such
names as " mock ore " and " false lead" has in recent years acquired
considerable economic importance in the Northern mining districts
(p. 162). In ore-deposits which contain both zinc and lead, like
those of the North, it is a matter of common observation that galena
may be found in the upper part of a vein, but that blende is not
reached until the deeper parts are worked. In a mixed ore-body,
the tendency seems to be for blende to increase in depth whilst
galena diminishes. Such a relation has been explained by Professor
Van Hise as due partly to the zinc-sulphide having been deposited

* Trans. Cwnb. Assoc., Part vii. (1882), p. 107.

166 MINERALS OF THE NORTHERN LEAD DISTRICTS.

from ascending solutions lower down than the lead sulphide, and
partly to a secondary concentration of zinc-sulphide by descending
waters.* Blende may be readily removed in a soluble form and
re-deposited at lower levels, but galena is one of the last sulphides
to go into solution.

Zinc is a metal very widely diffused in rfature. Dieulafait found
it in sea water, and it occurs in greater or less quantity in many
sedimentary rocks, especially limestone. Crystals of blende are
not uncommon in the fissures of nodules of clay ironstone, notably in
those from the Coalbrookdale coal-field, as seen in Wall-case 24, and it
occurs even in the casts of fossil shells (No. 1009). In the Cleveland
iron-ore, an altered sedimentary deposit of the Middle Lias, zinc
may be found, and Mr. J. Pattinson obtained considerable
quantities of the oxide from the waste-gas tubes of blast-furnaces
smelting this ore.f Oxide of zinc, in hexagonal prisms, has also
been found in connection with the furnaces at Westbury-on-Severn,
where iron ore from the Coral Rag was smelted. Mr. Fox-Strangways
has pointed to the rather common occurrence of zinc-blende in the
Lias, especially in the doggers in the upper part of the Lower Lias,
where it is associated with organic remains. J Zinc blende has
occasionally been found in old mine-timber.

In such cases the sulphide has probably been reduced by organic
matter from the sulphate, a very soluble salt which itself has gener-
ally been formed from the oxidation of blende. In other cases the
zinc may have been transported as a solution of carbonate, from
which, on mingling with waters containing sulphuretted hydrogen,
zinc sulphide would be precipitated.

Only a few specimens of zinc-blende are exhibited in this Case.
Crystals of blende are associated with quartz in No. 1196 ; with
calcite in No. 1194; with pearl-spar in Nos. 1195 and 1200 ; with
chalybite in No. 1202 ; and with pyrite in No. 1 197. In the specimen
No. 1199, crystalline blende occurs as a large hemispherical mass,
with radial structure, in association with deep purple fluor-spar
and partly encrusted with pearl-spar. A, similar specimen, from
the old lead-mines of Allenheads, will be found in Wall-case No. 28.

Calamine, etc. (Nos. 1203 to 1206).

The characters of Calamine, or zinc carbonate, have already been
noticed in connection with the specimens from Derbyshire in Case
VIII. (p. 141). The representatives of this species from Alston
Moor, coupled with some excellent examples from the same locality
in Wall-case 33, serve to show the mineral in mammillary deposits,
evidently thrown down from solution, rather like a zinciferous
stalagmite. Sulphate of zinc, resulting from the oxidation of blende,
if carried in solution through the limestone, would suffer decomposi-

» * " Some Principles Controlling the Deposition of Ores." By C. R. Van
Hise. Trans. Am. Inst. Miti., Eng., vol. xxx. (1901), p. 27.

t Rep. Brit. Assoc, for 1863, p. 49.

J Mem. Geol. S,urv. Jurassic Rooks, vol. i. Yorkshire, (1892), p. 473.

CHALYBITE, ETC. 1G7

tion ; during its percolation and in the presence of an excess of
carbonate of lime, or under certain other conditions, the carbonate
of zinc might be precipitated, whilst sulphate of lime would be
carried away in solution.* The calamine might thus either replace
the limestone, as already mentioned (p. 141), or be deposited in free
spaces, like a calcareous dripstone. No. 1204 shows the calamine
in staladitic, and No. 1205 in stalagmitic forms.

As small quantities of copper-ore occur in the limestone of the
Northern lead-and-zinc districts, and have indeed been occasionally
worked, it is easy to understand that carbonate of copper might
enter into association with carbonate of zinc, with production of
such a mineral as Aurichalcite. The specimen from Nenthead (No.
1206) may be compared with that from Roughten Gill (No. 1155,
p. 158).

Chalybite, Pyriie, etc. (Nos. 1207 to 1215).

Chalybite, or siderite, is present in many of the ore-deposits of
the Northern lead districts, often occurring in the sparry or crystal-
line state of spathic iron-ore, forming the mineral of the vein-stuff,
or gangue, usually in a fault-breccia, and in many cases converted
more or less completely into limonite. The fine spathose ore of
Weardale recalls the similar ore of the Brendon Hills. It is, as is
usually the case with such ores, manganiferous, and has been
valued for the production of spiegeleisen and ferro-manganese.
Mr. A. Dick remarks that the Weardale ore which he examined,
on solution in hydrochloric acid, left a skeleton of quartz having
the shape and size of the original mass.f

In No. 1209 cubes of purple fluor-spar are coated, on certain sides
only, with an incrustation of the carbonate of iron in brown lenticular
crystals. Other specimens of like character, but of larger size, will
be found in Wall-case 30.

Chalybite is a mineral which appears to be of late introduction
in the lead-veins of the Alston district, as pointed out by Sir W. W.
Smyth. Its recent formation is illustrated by its occurrence as an
incrustation on an iron rod in one of the mines. J Fossils have been
found in which the calcareous parts were represented by carbonate
of iron, and the mineral appears in many cases to have been formed
by alteration of the limestone. Mr. J. G. Goodchild has suggested
that the replacement has been effected by means of iron-bearing
solutions filtering downwards from the New Red strata which at
one time probably covered the Carboniferous rocks. §

A few specimens exhibited here represent the two types of iron
disulphide — pyrite, the common cubic type (Nos. 1210 to 1212),
and marcasite, the orthorhombic species (Nos. 1213 and 1214). A
third species of iron sulphide called Pyrrhotite, or often Pyrrhotine,

* See L. Hoffman in Journ. f. Prakt. Geol. Feb. 1896, p. 51.
* f Mem. Geol. Surv. " The Iron-ores of Great Britain." Part i., 1856, p. 58.
j, % Quart. Journ. Sc, voL v., p. 36.

§ Trans. Cumberland Assoc, vol. viii. (1883), p. 200.

168 MINERALS OF THE NORTHERjn WSAD DISTRICTS.

is represented by No. 1215, a specimen from Smittergill Head. This
species differs from the other sulphides of iron (1) in crystallizing
in the hexagonal system, (2) in presenting a bronze colour, and (3) in
possessing magnetic properties, whence it is often called magnetic
pyrites.

Barytes (Nos. 1216 to 1234).

Some of the finest crystals of Barytes, or Barite, found anywhere
in Britain have been obtained from the neighbourhood of Alston
Moor, especially from Dufton Fell in Westmorland. It was
this locality that yielded the huge crystal, weighing a hundredweight,
which is placed in the Case'^beneath Section I. of the Horse-shoe
Case. This specimen, believed to be the largest crystal of barytes
ever recorded, was shown in the Great Exhibition of 1851. Some
colourless pellucid crystals of similar type, probably from Silver -
aband, are exhibited in this Case (Nos, 1221, 1222).

Barytes crystallises in the orthorhombic system, and the crystals
exhibit much variation of habit, being frequently prismatic by
extension in the direction of one or other of the axes. Tabular
crystals are common. The specimen No. 1225 is a cleavage-frag-
ment, the mineral giving perfect cleavage parallel to what is re-
garded by some as the basal pinacoid, by others as the brachy-
pinacoid, and less perfect cleavage in two other rectangular direc-
tions. The rainbow-coloured !bands in Nos. 1217 to 1219 are an
optical effect, due to the narrow cleavage cracks in the specimens
giving the interference-tints of thin plates.

Crystals of barytes often resemble those of celestite, the sulphates
of the closely related metals, barium and strontium, being iso-
morphous. The relation of barium to lead is also in many ways
very intimate — closer indeed than its relation to calcium. This is
illustrated by the isomorphism of the sulphates and carbonates —
barytes being isomorphous with anglesite, and witherite with cerus-
site. On the contrary the relation of barytes to anhydrite, or cal-
cium sulphate, though the latter is also orthorhombic, is much less
marked. A small proportion of strontium and calcium sulphate
may be present in barytes.

In the Northern lead veins, as in those of Derbyshire (p. 136), the
barytes frequently appears in the form of cawk, a variety which is
either earthy or is in opaque white curved lamellae. The rounded
groups of tabular crystals are sometimes called crested or cocks-
comb barytes (No. 1230). A curious habit is exemplified by No.
1224, in which tabular crystals are disposed in a divergent group,
like the partly-opened leaves of a book. The well-known chisel-
edged crystals, from Alston Moor, are illustrated by No. 1223. In
consequence of its high density, for a sparry mineral, barytes is often
known as heavy spar (specific gravity 4 • 3 to 4 • 5).

As far back as 1851 Dieulafait called attention to the wide dis-
tribution of barium and strontium ; and in recent years these ele-
ments have been recorded as occurring in a great number of rocks

169

and in many natural waters. According to Mr. F W. Clarke and
Dr. Hillebrand, barium forms about 0*03 to CKJ4 per cent, of the
crust of the earth.* A large number of analyses, showing how
widely barium is disseminated through rocks, have been collected
by R. Delkeskamp.f

Since many igneous rocks contain barium, especially in their
felspathic constituents, it has often been held that the barytes
of certain mineral-veins may have been derived from the minerals
of the neighbouring rocks. It was shown, for instance, by Sand-
berger that the veins of barytes in the granite of the Black Forest
became thicker and more abundant in proportion as the felspar
of the granite was richer in barium, whilst similar veins were even
better developed in the gneiss of the district, in which the felspar
contained as much as - 81 per cent, of barium.

It has been observed that barytes tends to become localised in
the upper part of many mineral deposits and to disappear in depth.
Possibly in such cases oxidising influences may have converted
barium sulphide into the insoluble sulphate. In other cases, barytes
may have been precipitated by the action of soluble sulphates,
like that of iron resulting from the decomposition of pyrites, on
certain barium minerals in the neighbouring rocks.

Considering the extreme insolubility of sulphate of barium, it
is interesting to cite a case, to which Mr. Goodchild has called atten-
tion,! in which crystals of barytes from Dufton had been invested
by calcite, and then removed, leaving the calcite-crusted cavity
empty. It would seem then that the calcite, generally so easy of
solubility, has withstood the attack of some solvent potent enough
to carry off the intractable barytes. Several specimens here show
the association of barytes with calcite (Xos. 1230 to 1234).

Some remarkable instances of the occurrence of barium salts in
natural waters will be referred to in connection with the barium-
bearing sandstones of the Trias (p. 187).

* Bull. U.S. Owl. Surv., No. 148, 1897, p. 13.

f " Die weite Wrbveitung des Baryums in Gesteinen und Mineral quellen
und die sich hieraus ergebenden Beweismittel fur die Anwendbarkeit de-
Lateralsecretions-und Thermaltheorie auf die Genesis der Schwerspathgange."
ZeMs. f. Prakt. Geolog., April 1902, p. 117.

% Trans. Cumb. Assoc, vol. viii. (1883), p. 100.

7SS2.

170 MINERALS OF THE NORTHERN T.^ATT,

CASE X.

DIVISION 1.
MINERALS OF THE NORTHERN LEAD DISTRICTS.

SPARS OTHER THAN HEAVY SPAR.

Witherite (Nos. 1235 to 1246).

Although, barium most commonly occurs in nature as a sulphate,
it is also found not infrequently in the condition of a carbonate.
Some excellent specimens of the crystallised carbonate, from Cum-
berland and Northumberland, are here exhibited. So far from
being a mineral of only scientific interest, carbonate of barium
is a substance of considerable economic value, occurring in rather
extensive deposits and finding application in several ways in the
industrial arts. During the year 1902 as much as 6,142 tons,
valued at £12,284, were raised in Northumberland.

Barium carbonate was first recognised as distinct from barytes
by Dr. W. Withering,* who examined it chemically more than a
century ago, and described it, according to the chemical language
of his day, as terra ponderosa aerata, or " aerated barytes." In
his honour the mineral was named Witherite by Werner. It crystal-
lises in the orthorhombic system, and is isomorphous with aragonite,
strontianite, and cerussite, these four species constituting a group
characterised by similarity of crystalline form, of cleavage, and of
optical properties.f A rather large and fine series of witherite
crystals is here exhibited.

Crystals of witherite usually have a pyramidal habit, and the
pyramids are often pseudo-hexagonal, so that the aspect of the
mineral is rather suggestive of that of quartz. These hexagonal
bi-pyramids are not simple crystals, but are really triplets, and
their complex structure is revealed on section. The faces are
often rough, with horizontal striations, and may carry a thin
coating of opaque white barytes. Bischof showed that if
water holding sulphate of calcium in solution passed over
witherite it would give rise to sulphate of barium and carbonate
of calcium. Solutions of other sulphates produce similar reactions.
Hence it often happens that barium-bearing deposits carry the
sulphate above, where superficial waters have been at play, and
the carbonate below.

* " Experiments and Observations on the Terra Ponderosa, etc." By
William Withering. Phil. Trans., vol. lxxiv. (1784), p. 293.

j See Table showing the relationship in Tschermak's Lehrbuch der Minera,-
logie, 4, a6\, 1S94, p. 259.

)CALCITE. 171

Witherite appears to have been first discovered by James Watt
at Anglezark Moor, near Chorley, in Lancashire. Here the lode,
running through the Kinderscout Grit (Millstone Grit) yields galena,
blende, and copper-pyrites. Witherite is also found at Alston
Moor, but the chief localities are Fallowfield Mine, near Hexham,
in Northumberland, and Settlingstones in the same county ; the
last named is at present the most extensive producer of the mineral.

Like all barium salts, witherite is poisonous. Fowls have
frequently been killed in the neighbourhood of the mines by picking
up fragments of the mineral. It is a constituent of certain rat-
poisons, and is employed as a source of various preparations of
barium. Witherite has also been extensively used in sugar -refining,
but owing to its poisonous character it has been displaced to
a large extent by strontium carbonate. Glass-making is another
industry in which witherite has found limited application. Josiah
Wedgwood employed it in the manufacture of his delicate ' jasper
ware.'

Bromlite and Barytocalcite (Nos. 1247 to 1254).

As far back as 1837 the name Bromlite was given by Dr. T. Thom-
son to a mineral from Bromley Hill, near Alston ;* but this name
was set aside by many writers in favour of the term Alstonite.
Recent regard for priority has, however, led to the revival of the
older term.

The mineral called bromlite or alstonite, whilst commonly regarded
as a double carbonate of barium and calcium, seems to be an
isomorphous mixture of the two salts. Although belonging
to the orthorhombic system, its crystals are usually small acute
bi-pyramids of hexagonal habit, somewhat resembling those of
witherite. In some specimens, the crystals have a slight pinkish
tint, perhaps due to a trace of manganese. Strontium carbonate
is recorded in some of the analyses.

Another mineral of similar composition is known as Barytocalcite —
a name given to it by Mr. H. J. Brooke in 1824 (Ann. Phil.,
vol. viii., p. 114), but as tip's crystallises in the monoclinic
system, it is difficult to see how it can be brought into direct
relationship with either the calcite group or the aragonite- witherite
group of minerals. The crystals of barytocalcite commonly
have a prismatic habit, and are disposed in divergent groups. In
some cases they bear a superficial coating of barytes.

According to Analyses by A. Becker,"]" barytocalcite seems to be
a definite molecular compound, conforming to the formula
BaC0 8 .CaC0 3 , thus differing essentially from bromlite. Such a
view indeed had previously been expressed by Prof. Groth.J

* Phil. Mag., vol. xi. (1837), p. 45, see also ibid., vol. vi. (1835), p. 1 ;
and vol. x. (1837), p. 373.

t " Ueber die ch?mische Zusammensstzung des Barytocalcits und des
Alstonits." Zeit8. f. KrysL, vol. xil. (1887), p. 222.

J " Tabellarische Uebersioht."
7882 >•' 2

172 MINERALS OF THE NORTHERS- ' "■-> * ~

Both bromlite and baryto-calcite are minerals of very local
distribution, being confined to Alston Moor and the neighbourhood
of Hexham. Some of the finest examples of bromlite have been
yielded by the Fallowfield Mine, near Hexham, which is famous
for its witherite.

Calcite and Aragonite (Nos. 1255 to 1312.)

A rather extensive series of specimens illustrates the varieties
of form and other physical characters presented by the Calcite of
the Northern lead-mining districts. Calcite is a species unparal-
leled for its wealth of crystalline forms. Count de Bournon, in the
early part of the nineteenth century, recognised several hundred
modifications ; * and in recent years the crystallography of the
species has been the subject of exhaustive study by several observers.
Mr. J. R. Irby in 1878 recorded no fewer than fifty rhombohedra
and 155 scalenohedra."j"

Many of the Cumberland specimens here exhibited recall the
calcites from the lead-bearing limestones of Derbyshire displayed
in Case VII. (p. 132), but a comparison of the two collections never-
theless reveals considerable difference in the facies or general appear-
ance of the groups. A casual glance is sufficient to suggest that
whereas, broadly speaking, scalenohedra dominate in Derbyshire,
the Alston specimens show a prevalence of obtuse rhombohedra
constituting what is known as the " nail-headed " type of calcite.

The cause of the differences in the habit of the calcite crystals
is not easy to explain, but it seems connected with the conditions
under which crystallisation occurred, especially with the character
of the solution from which the substance crystallised. Some inter-
esting researches have been carried out in recent years by Heinrich
Vater J with the view of throwing light on this obscure subject.
He concludes that from a pure solution in water, calcium carbonate
crystallises in the fundamental rhombohedron, and that the occur-
rence of other forms is referable to the presence of co-solutes, that is
to say, other substances in the solution from which crystallisation is
effected. Sulphates were found "to exert considerable influence,
and sulphate of sodium so modified the calcite crystals that they
assumed the form of hexagonal prisms with rhombohedral termina-
tions. The influence of the co-solute seemed to increase when the
crystallisation took place, as it probably does usually in nature,
very slowly.

Although no specimens of crystallised Aragonite are exhibited
among the Alston minerals, there is a fair example of that
particular variety which is known, rather strangely, as flos Jerri,

* " Traite de Mineralogie." Premiere Partie. 3 vols. London, 1808.

f " On the Crystallography of Calcite." Inaugural Dissertation. Bonn.
1878. Dr. Irby died in 1880.

% An excellent summary of Vater's papers, by Dr. A. Hutchinson, will be
found in the Min. 3iaj. for Dec, 1903, p. 392. The originals appeared in the
Zeils. j. Kryst., from 1893 to 1S99.

ARAGOXITE, ETC. 173

or iron-bloom (No. J 307). This form of aragonite occurs as
arborescent masses, with interlacing stems and branches, fibrous
in structure, and snow-white or creamy in colour. From the re-
semblance of some of these white sprigs to certain kinds of coral,
the form is recognised as " coralloidal." Though called " flower of
iron, the Cumberland mineral occurs not in iron-mines but in
cavities in the limestone near to the veins of lead-ore, and it was
formerly rather abundant at the Dufton Mines. The conditions
of its occurrence were studied many years ago by Mr. W. Wallace,*
who suggested that the growth of the mineral was due to a circula-
tion of fluids through its pores. It occurs only above water-level,
where the conditions are favourable for the precipitation of carbonate
of lime, and the formation of stalactitic and stalagmitic deposits.

Fibrous forms of carbonate of lime are known from the lustre
which they display, especially when polished, as " satin-spar " — a
name which is applied, however, to several fibrous minerals, in-
cluding calcite, aragonite, and gypsum. Xos. 1305 and 1306 are
excellent examples of satin-spar from Alston Moor ; the latter
specimen, which is polished, illustrating the occurrence of the
mineral as veins in black shale. It is often assumed that such
fibrous carbonate of lime is necessarily aragonite, but Mr. L. J.
Spencer has shown by optical examination of the Alston spar, as
also by its density, that it is really composed of calcite, each fibre
being a crystal of calcite enormously elongated in the direction of
a rhombohedron edge.f It has been shown, moreover, by Dr.
G. P. Merrill that most of the stalagmitic carbonate of lime known
as onyx marble is not aragonite, as is frequently supposed, but
really calcite. %

The specimen Xo. 1309 shows delicate pearly scales of carbonate
of lime, such as is known to German mineralogists as Schaumkalk.
It is often regarded as an alteration-product, due to the conversion
of gypsum into a carbonate, like aragonite.

A few specimens exhibited here (Nos. 1310 to 1312) illustrate the
occurrence of Dolomite, or pearl-spar, among the minerals of the
lead deposits of Cumberland. The characteristic specimen Xo.
1310 shows the spar in a crowded group of small cream-coloured
rhombohedral crystals, with curved faces and nacreous lustre,
seated on galena. In Xo. 1311 there is a similar aggregate of
curved or saddle-shaped crystals, upon which calcite has crystallised
in a linear group of obtuse rhombohedra. §

* ' On the Growth of Flos Ferri, or Coralloidal Arragonite." Quart. Journ.
Cleol. Soc., vol. xxi. (1865), p. 413.

"(■ " The ' Satin-spar ' of Alston in Cumberland ; and the Determination of
massive and fibrous Calcites and Aragonites." Min. Mag., vol. xi. (1897),
p. 184.

% Smithsonian Report (Tj.S. Nat. Mus.) for 1893-4, p. 539.

§ On the subject of dolomitisation see Prof. Judd's researches in Report
of the Coral-Reef Committee of the Royal Society, Section xii. 1904. See
also Dr. Skeats in Bull. Harvard Coll., xlii. ; geol. series, vol. vi-, No.
2, 1903.

174 MINERALS OF THE NORTHERN LEAD DISTRICTS.

DIVISION 2.
MINERALS OF THE NORTHERN LEAD DISTRICTS, ETC.

THE SPARS, CONTINUED.

Fluorite {Nos. 1313 to 1352).

' Some of the finest known crystals of Fluorite have been obtained
from the Northern lead-mining districts, especially from the mines
of Weardale in Durham. A rather large series of representative
specimens is here exhibited, including many crystals which rival
the fluors already described from Derbyshire, Cornwall, and Devon
(pp. 85, 134).

The Northern fluors are generally crystallised in simple cubes,
which in most cases are boldly and symmetrically developed. Oc-
casionally, however, the cube is extended along one axis, so that
some of the faces become long rectangles : such a parallelopipedon
is well seen in No. 1313 — which is a specimen of purple fluor from
Weardale in Durham, with small crystals of calcareous spar
perched upon the faces of the larger crystal.

Several of the specimens show the characteristic interpenetration
of two cubes. The three-faced solid angles of one cube are seen
jutting out from the faces of the other, in such specimens as Nos.
1314 to 1316. In these penetration-twins it would be possible to
bring one of the cubes into the position of the other by giving it
half a complete turn, or rotating it through 180°, round an axis
running from one quoin of the cube diagonally to the opposite
quoin : in other words, the twin axis is a cube-diagonal, or a normal
to the plane of an octahedron.

Considerable diversity of colour is presented by the specimens
of fluorite here exhibited. Some of the finest Alston and Wear-
dale fluors are of violet or purple colour (Nos. 1314 to 1320), whilst
those from Weardale are often of green tints (Nos. 1323 to 1328).
Many years ago Wyrouboff referred the colour of many fluors to
the presence of organic matter, and thus explained the tinctorial
change which the mineral not uncommonly suffers when heated.*
The pigment in some cases is certainly fugitive. More recently
the studies of K. v. Kraatz-Koschlau and Lothar Wohler have sup-
ported Wyroubofl's views. They found in a violet fluorspar from
Weardale 0-01 per cent, of carbon and 0-008 of hydrogen, in blue
and green fluors from Cumberland 0-009 of carbon and 0-002 of
hydrogen, and in yellow fluor from Durham 0-007 of carbon and
■ 0025 of hydrogen ; whilst the colourless fluor was free from either
of these elements.-)- The organic nature of the colouring agent

* " Sur lea Substances Colorantes des Fluorines." Bull. Soc. Chim., vol.
v. (1866), p. 334.

" Die Naturlichen Farbungen der Mineralien." Min. 2iit., vol xviii
1899), pp. 304, 447.

FLUOR-SPAR. 175

has been denied by E. Weinschenk, who holds that the presence of
a hydrocarbon in the fluor does not necessarily prove that the hydro-
carbon is responsible for the colour.*

Some of the Cumberland fluorite is remarkable for its beautiful
fluorescence. Whilst the mineral may appear violet or purple or
bluish by reflected light, it becomes pale green when viewed by
transmitted illumination. The phenomenon of fluorescence was
so named by Stokes in consequence of its exhibition by this mineral.
Now that the existence of certain hydrocarbons in fluor is recognised,
it has been suggested that the fluorescence may be connected with
their presence, since it is well known that fluorescence is strikingly
exhibited by certain substances of this nature, such as petroleum,
and by ozocerite and some kinds of amber, like the Sicilian simetite.

The phosphorescence of fluorspar has been noticed in connec-
tion with the Cornish specimens (p. 88). The Cumberland fluor
is in certain cases markedly thermophosphorescent. It may be added
that fluorite is found to phosphoresce under the influence of the
Rontgen rays.

Some of the green cubes of fluorite from Weardale are remarkable
for enclosing cavities holding liquid, with a vapour-bubble, mov-
able like that of a spirit-level. According to Greg and Lettsom,
these liquid drops are most frequent in cubes which have a dull
greasy look, especially in such crystals as have the edges bevelled.
Paper arrows indicate the position of the moving bubble in the
specimens in the tray No. 1324.

So much has already been said with reference to fluorspar that
little need now be added. The specimens in this compartment
may serve to illustrate the characteristic associations of the mineral
in the ore-deposits of the country near Alston. The fluorite is
associated with calcite in No. 1351, with barytes in No. 1339,
with quartz in No. 1354, with galena in No. 1340, with blende in
No. 1342, and with chalybite in Nos. 1343 to 1348. An interesting
formation is represented by the specimen No. 1352, in which fluorspar,
crystallising in an aggregate of pale purple cubes, is coated on certain
faces only with quartz, upon which there is a sprinkling of minute
crystals of chalcopyrite. In No. 1353 the cubes of fluor are extended
along one axis, and are coated with minute crystals of quartz, form-
ing a drusy surface.

In No. 1349 the following succession may be noted : (1) fluorite
in large violet cubes ; (2) galena, in cubo-octahedra built up by the
confused aggregation of sub-individuals ; (3) calcite in low rhombo-
hedral crystals. Here the fluorspar is of earlier formation than
the galena, but in other cases, as in No. 1328, the fluor may be of
later growth.

It is well known that calcium fluoride is slightly soluble in water
containing acid carbonate of calcium. It is, however, soluble to
an appreciable extent even in pure water. According to Kohlrausch

+ " Naturlich Farbungen der Mineralien." Min. Mitt., vol. xix. (1900),
p. 144.

17G MINERALS OF THE NORTHERN LEAD DISTRICT.

and Rose, who determined the solubility by the electric conduc-
tivity of the solution, fourteen milligrams of fluorspar were dis
solved in a litre of water at 15° C*. It is, in fact, more soluble
in pure water than calcite. Hence it is not difficult to understand
how it comes about that many natural waters contain fluorine as
a calcium compound, and that fluorite may migrate in mineral
deposits, and be precipitated at different stages in the history of
vein-formation.

Fluorspar occurs in such abundance as a veinstone in the lead
districts of the North of England that it is worked on a commercial
scale. In the year 1902 the county of Durham yielded as much as
3,708 tons of spar, valued at £l,417.t This was raised in the neigh-
bourhood of Stanhope in Weardale. The economic uses of fluor-
spar have been mentioned in the notice of the Derbyshire minerals
(p. 185).

So prolific aif the mineral deposits of the Northern lead districts
in fine examples of fluorspar that in addition to the large series
shown here, other specimens from the same localities, including
some larger pieces, will be found by the visitor in the Ludlam Col-
lection displayed in the Hall and in Section M of the Horse-shoe
Case.

Quartz (Nos. 1353 to 1360).

Whilst fluorspar, barytes, and calcite are the principal gangue-
minerals in the lead-lodes of the Northern counties, Quartz also is
occasionally found in the vein-stuff of certain deposits. On the
eastern side of the Hall of the Museum, the visitor will find a pedestal
supporting a huge mass of well -crystallised white quartz from the
lead mines of Weardale in Durham — an imposing specimen, which
was shown, as an exceptional example of this mineral, in the Great
Exhibition of 1851.

Only a few specimens of quartz are here exhibited, and these
are not to be compared for beauty with the crystals from the haema-
tite deposits of West Cumberland, displayed in Case VIII. (p. 148).
In the fluor-bearing veins, the quartz has evidently been formed
at different stages in the history of the deposits. Thus, in No. 1354
the quartz is well crystallised in six-sided pyramids, and upon these
crystals some beautiful cubes of fluorite, remarkable for their delicate
purple tint, have been deposited. On the other hand, No. 1355 shows
a growth of pellucid crystals of quartz on cubes of yellow fluor. In
the former specimen, then, the formation of the quartz was anterior,
and in the latter posterior, to that of the fluorspar. Nor are these
cases exceptional. The examination of other specimens in the collec-
tion will show that in some cases the quartz forms the seat of the
fluor. and in other cases encrusts it. So too with the galena. Quartz

*F. Kohlrausoh and F. Rose in Zeits. f. Phy. Ch., vol. xii. (1893), p. 162.
Quoted in Braun's " Chcmische Mineralogie," 1896, p. 397.

t Home Office Report on Mines and Quarries for 1902. Edited bv Sir C. Le
Neve Foster, F.R.S., p. 209.

MINERALS OF SHROPSHIRE. 177

crystals may support a deposit of lead-ore, as in No. 1354, or a
growth, of quartz may have occurred on the ore, as in No. 1357.
Successive generations of quartz crystals may be observed on such a
specimen as No. 1355, where quartz has preceded and also succeeded
the formation of fluorspar.

Very curious is the Cellular quartz from Teesdale, specimens of
which are to be found in most mineral collections. It is illustrated
here by Xo. 1359, and another and larger specimen will be found in
the Horse-shoe Case. This brownish quartz forms an open honey-
combed structure, probably representing the siliceous septa of what
was once a septarium. Most septaria are composed of argillaceous
limestone, or of clay ironstone, which by contracting on solidification,
becomes fissured, and the cracks so formed are either left open or
are filled in, mure or less completely, by deposits of calcite, forming
radiating or reticulated septa. The crystalline calcite is usually
more durable than the substance of the nodule, and, therefore, on
weathering, the septa stand out in relief. In the flat nodule from
which such a specimen as No. 1350 has been derived, the shrinkage-
fissures, formed with great regularity, must have been filled with a
siliceous deposit, which has been left, as a kind of skeleton, after the
entire removal of the substance of the original septarium.

The small isolated crystals of quartz from Harrogate, No. 1360, recall
the similar crystals known as " Buxton diamonds," noticed on p. 136.

Minerals of Shropshire.

{Xos. 1361 to 1368.)

In the Shelve district — a tract of wild country in Shropshire,
near the Welsh border, consisting of rocks of Lower Silurian
(Ordovician) age — lead-ore has been worked from a very remote
period. Roman pigs of lead, found at, or near, the mine called Roman
Gravels, carry back the industry of the district to at least the second
century of our era. At the present time, however, there is but little
activity in connection with the metal mines of the county. In 1902
only 805 tons of lead-ore weie raised in Shropshire, and this was
yielded almost entirely by one mine — the Snailbeach near Minsterley.
This mine produced also 378 tons of sine-ore.

The lead -lodes of this district vary much in direction, but many of
them strike a little N. of west, and S. of east. They generally run
through dark slaty rocks associated with sandstones and shales, and
invaded by igneous intrusions. Many of the veinstones are brecci-
ated, consisting of fragments of the neighbouring rock cemented by
calcite, barytes and quartz. The ore generally occurs in " shoots,"
or i nclined bands, and consists of galena, blende and pyrites.

As the veins are not productive of many crystallised minerals, the
collection here exhibited is rather meagre. It includes samples of the
typical Galen a from Snailbeach (Xo. 1361) and of Cerussite, in fine
acicular crystals (No. 1362). The Salopian lead ore is not usually
argentiferous. Among the sparry minerals of the veinstone may be
mentioned the Snailbeach Calcite and several specimens of

178 MINERALS OF LEICESTERSHIRE.

Barytes. Some beautifully pellucid crystals of barytes from the
East Wotherton Mine, near Minsterley, presented by A. Steven, Esq.,
are here exhibited (No. 1367). They rather resemble some of the
crystals from Dufton. The Salopian barytes has been examined
crystallographically by Prof. Miers * and by Mr. C. J. Woodward.f

The specimen No. 1366 is an example of barytes from Snailbeach,
remarkable for its brick red colour, due to the presence of iron oxide.
When barytes is used as a white pigment every trace of iron has to
be removed — the removal being effected by boiling with dilute
hydrochloric acid.

Associated with the barytes of Shropshire, Witherite occasionally
occurs, as described by Mr. Aikin in the, early part of the last centuryj
According to this observer, it was found in irregular masses, often of
considerable size, embedded in the barytes, and was called by the
miners " yellow spar," because though appearing white by reflected
light, it became yellow by transmitted light. A specimen of the
fibrous witherite is here exhibited (No. 1368).

No. 1365 is an example of Asphalt, associated with calcite, from the
Pennerley lead mine, near Shelve. Bituminous minerals are occasion-
ally found in rock-fissures not only in the Shelve district and in the
Stiperstones, but in the yet older slaty rocks of the Longmynd,
regarded as pre-Cambrian. The late Dr. Ricketts believed that
these carbonaceous minerals were probably -derived from the Coal
measures. §

Minerals of Leicestershire.

(Nos. 1369 to 1380.)

The collection contains a few specimens from the mines which
were at one time worked near Ashby-de-la-Zouch, in Leicestershire.
These incude some examples of Calcite, crystallised in sharply defined
scalenohedra, much like the dog-tooth spar of Derbyshire, and pro-
bably formed under similar conditions. The calcareous spar is
associated in some of the specimens with Galena (No. 1371) and in
others with Chalcopyrite (Nos. 1372, 1376). In some cases the
copper-pyrites is sprinkled over the calcite, rather recalling the
association seen in certain specimens from Ecton.

Professor Hull remarks that the Carboniferous Limestone of Dim-
mingsdale is highly metalliferous, and records the occurrence, in one
of the veins, of copper-pyrites, galena, calcareous spar, sparry iron
ore, blende and bitumen.|| According to Prof. Bauerman, whom he
cites, the lodes are mostly brecciated, and the galena generally
occurs in ribs at each side of the walls, whilst the other minerals are
found crystallised in druses of the veinstone.

* " Nature," vol. xxix. (1883), pp. 29, 124. f Ibid -> P- 77.

% " Notice concerning the Shropshire Witherite." Trans. Oeol. Soc, vol.
iv. (1811), p. 438.

§ " On Bitumen in the Palseozoio Rocks of Shropshire." Proc. Liverpool
Oeol. Soc, 1885. For minerals of Shelve see G. H. Morton., ibid., 1869.

|| Mem. Oeol. Surv. " The Geology of the Leicestershire Coal-field," 1860,
p. 16.

MOLYBDENITE, ETC. 179

The specimen No. 1377 is a good example of the occurrence of
Asphalt at Staunton Harold, near Ashby-de-la-Zouch. Bituminous
minerals, in some cases solid and in others liquid, are not uncommon
in the cavities in the older fossiliferous limestones. The next specimen,
No. 1378, is interesting as showing a bituminous substance, associated
with calcite, which has crystallised in the joints of the granite of
Mount Sorrel, near Loughborough.

Another specimen from Mount Sorrel (Xo. 1379) illustrates
the occurrence of the rather rare mineral Molybdenite, or sulphide
of molybdenum, in the characteristic form of graphite-like crystal-
line plates, on the walls of joints in the granite. This speci-
men was presented by Sir C. Le Neve Foster, who first called
attention to the occurrence of the mineral at this locality,* where it
was regarded by the quarrymen as " lead." The same species occurs
in the Shap granite, as remarked on p. 154.

The county of Warwick has furnished the specimen of the mineral
called after the classical name of the locality, Varviscite, and ex-
hibited here as No. 1380. Thi3 mineral was found in the deposits of
manganese ore which were formerly worked in the Cambrian rocks
of Hartshill. The name was given by Mr. Richard Phillips, on the
assumption that the mineral was a distinct species, but it is now
usually held to be merely a mixture of pyrolusite and manganite.
Mr. Phillips (b. 1778, d. 1851) was the first Curator of this Museum.

* " On the Occurrence of Molybdenite in Leicestershire, etc." Geol. Mag.,
vol. iii. (1866) p. 525.

180 MINERALS OF THE NEOZOIC STRATA.

CASE XI.

DIVISION 1.
MINERALS OF THE NEOZOIC STRATA.
Chiefly from the Midlands and S.E. England.
(Nos. 1381 to 1448.)

So far as Southern Britain is concerned, the principal mineral
districts are fairly represented — though with many gaps — in the
contents of the ten preceding Cases. The remaining minerals of
England find representation in that part of the Collection now to be
noticed, which is placed in the first half of Case XI.

Most of the mineral deposits of Britain occur in connection with
the Palaeozoic strata, or even with rocks still more ancient. The
minerals to be now described occur, on the contrary, in Neozoic
strata, that is, in the Secondary and Tertiary formations. With
the exception of the iron-ores, and a few other minerals, they are
not generally regarded as metalliferous. As a rule they are found
in bedded deposits rather than in veins, and are not usually so well
crystallised as the vein-minerals, though occasional exceptions may
be cited, notably in the case of gypsum. A few of these minerals
have already been noticed ; thus, some of the products of the Trias
have naturally enough taken their place among the minerals of the
Bristol district. But these are exceptional. Most of the minerals
previously described have been derived from deposits in the older
rocks, though it by no means follows that the formation of the
mineral itself is of equal antiquity with that of the rock in which
it occurs. The rock may belong to one period ; the deposit which
it encloses to quite another. It has been already remarked, for
example, that certain mineral deposits in the Carboniferous rocks
may be of Tertiary age. In the case, however, of many of the
minerals which occur in the later sedimentary rocks, it is probable
that they were contemporaneous, or nearly contemporaneous, with
the rock which acts as the matrix.

In the arrangement of the Neozoic minerals, a strictly topographi-
cal arrangement has not been adhered to, since it would naturally
have led to much repetition of description, where a common species,
like gypsum> occurs in many localities at several distinct horizons.
A conveniently elastic arrangement has therefore been followed —
partly stratigraphical, partly mineralogical, but without pretence
to scientific precision.

18]

Halite or Rock-salt (Nos. 1381 to 1383).

At the base of the Neozoic strata, according to ordinary classifica-
tion, stands the Trias, and of all the minerals yielded by the Trias
of this country the most important is Rock-salt, or, as it is generally
termed by modern mineralogists, Halite. Extensive deposits of this
mineral occur near the base of the Keuper Marl. It usually forms
lenticular beds, varying in thickness from a few inches to upwards
of 100 feet. In some parts of Cheshire the rock-salt is mined, but
in most salt-works the substance is obtained from brine, which has
dissolved the salt from the saliferous marl. In consequence of the
abundance of salt the New Red Sandstone was termed by the early
geologists the '" Saliferous system." Although salt in this country
is practically limited to the Triassic and perhaps Permian strata,
important deposits occur in other parts of the world at various
geological horizons, some of the most notable Continental deposits
being of Tertiary age.*

Pure halite, as seen in Xo. 1381, is a colourless pellucid mineral,
crystallising in the cubic system, and presenting perfect cubic
cleavage. Usually, however, it is coloured more or less deeply,
as exemplified by the brown specimen Xo. 1382, the colour being
here referable to mechanical association with oxide of iron — a sub-
stance very widely distributed throughout the Triassic strata.

The salt may be regarded as contemporaneous with the Keuper
marl in which it occurs, and it has no doubt been deposited by the
evaporation of salt water. Possibly an arm of the sea may have
been cut off so as to become almost land-locked, as in the case of
the Kara Boghaz, or " Black Gulf " — a great sheet of water on the
eastern side of the Caspian, almost separated by a sand barrier
from the general body of water, and forming around its margin
a kind of natural salt-pan. It seems more likely, however, that in
most cases the salt was deposited in areas of inland drainage, where
the waters, destitute of any outlet, would become concentrated when-
ever the quantity lost by evaporation greatly exceeded the supply of
fresh water. The Great Salt Lake of Utah and the Dead Sea are
known to have shrunk in volume from this cause, so that the water
has gradually become more and more sahne.f Such inland sheets
of salt water probably present a parallel, as suggested by Sir A. C.
Ramsay, to the lakes in which the rock-salt was deposited.! On
the whole, the physical conditions of the British area during the
period of salt formation in the New Red Sandstone age may have

* See Sir A. C. Ramsay's Presidential Address to the British Association
at Swansea (1880) : " Salt and Salt-lakes," p. 9.

t V. 8. Geol. S>irv. Mon., No. I. By G. K. Gilbert, 1890 ; and No. XI. by
I. <J. Russell, 1885.

- & " The Physical Geology and Geography of Great Britain." By the late
Sir A. C. Ramsay, LL.D., F.R.S., 6th Ed. by H. B. Woodward, F.R.S., 1894,
p. 128. Also Ramsay's paper " On the Physical Relations of the Now P*ed
Jkjarl.," etc. Quart. J own. Geol Soc, vol. xxvii. (1871). p. lsO.

182 MINERALS OF THE NEOi 7 -"' ~r«-\v' : .«

been not dissimilar to the conditions which obtain at the present
time in such countries as Central Asia, where salt lakes occur in a
comparatively rainless or desert region.

Cubic cavities in certain rocks attest the former presence of
crystals of salt, and in many cases such cavities have been filled
in with mud and other mineral matter so as to form natural casts
in the cubic moulds. Pseudomorphous crystals of this character
are shown in the specimen No. 1383 from the Keuper marls of
Cheshire.

Rock-salt is worked to a limited extent in Cheshire and Lanca-
shire, but the amount yielded in 1902 was only 129,664 tons. On
the other hand, the salt obtained from brine springs in England,
whether natural or artificial, including the salt contained in the
brine run direct from the wells to the alkali works, amounted in the
same year to as much as 1,719,625 tons. These brine springs are
situated in Cheshire, Staffordshire, Worcestershire, Lancashire,
Yorkshire, and Durham. *

With regard to the age of the salt deposits of North-East York-
shire and South Durham, discovered about forty years ago by
borings in the Tees valley, there is some difference of opinion, since
certain authorities regard them as Permian, whilst others hold
them to be of Triassic age.f

Gypsum {Nos. 1384 to 1399).

In association with the rock-salt of the New Red Sandstone,
Gypsum is almost invariably found. Although gypsum frequently
occurs elsewhere unaccompanied by salt, the salt is rarely found
without gypsum, and such a relationship must be more than acci-
dental. If sea-water be evaporated under the microscope, it is
seen that acicular crystals of gypsum are first formed, and then
followed by little cubes of salt. Fractional crystallisation of a
similar nature occurs in salterns and salt-gardens, where there is
always a tendency for the sparingly soluble gypsum to be deposited
before the chloride of sodium. It is believed, however, that the
deposition of gypsum in marine lagoons may be partly due to the
action of certain bacteria. J

Much of the Triassic gypsum occurs in the crystallo-granular
form of Alabaster — a material extensively used for internal orna-
mental sculpture, especially in ecclesiastical architecture. Being
so soft as to be scratched even by the finger-nail, it is readily wrought
into elaborate forms, whilst the associated oxide of iron produces
on the polished face of the stone a pleasing effect by its veins and

* Home Office Report, Mines and Quarries, for 1902, p. 264.

f " On the Stratigraphical Position of the Salt-measures of South Durham."
By Prof. G. A. Lebour. Hep. Brit. Assoc, for 1886 (Birmingham), p. 673." On
thi Durham Salt Distriot." By E. Wilson. Quart. Journ.Geol.Soc., vol. xliv.
(1888), p. 761. "The Cleveland and S. Durham Salt Industry." By John
ilarley. Trans. Fed. Inst. Min. Enq., vol. i. (1892), p. 339.

JC.Barrois. Ann. Soc. Geo!. Nord., vol. xxvi. (1897), p. 19.

183

cloudings. Many examples of carved alabaster are exhibited in the
Hall ; and the walls of the Vestibule of the Museum are lined with
slabs of this decorative stone.

The gypseous marls of the Trias have been largely worked for
sake of the alabaster at Fauld in Staffordshire, at Chellaston in
Derbyshire, and at Newark in Nottinghamshire. According to
Mr. Metcalfe the mineral occurs in thick, nodular beds or " floors,"
in small lenticular masses or " cakes," and in globular or spheroidal
masses called " balls " or " bowls." * The granular gypsum may
be snow-white (No. 1385), or dull grey (No. 1386), or pink (Nos. 1387,
i 388). Some of these specimens are from Triassic marls at
Watchet on the north coast of Somersetshire, and others from the
neighbourhood of Penarth, south of Cardiff.

In certain veins running through the gypseous marls the
mineral occasionally occurs in a fibrous form, and is then known
as Satin-Spar— a name applied also to fibrous calcite, as already
explained (p. 173). Some examples of fibrous gypsum, mostly from
East Bridgford, in Nottinghamshire, are exhibited here (Nos. 1389-
1390), whilst others, illustrating its aspect when cut and polished, are
shown in Section H of the Horse-shoe Case. Like all substances
composed of parallel fibres, the spar, when cut with a convex surface,
exhibits a luminous band running at right angles to the direction
of the fibres. The beads in the Horse-shoe Case illustrate this
appearance. A curiously foliated variety of gypsum from the New
Red marl of Seaton in Devonshire, is shown in No. 1384 — a speci-
men presented by the late Sir W. C. Trevelyan.

Gypsum is sometimes known as P Ulster stone in consequence of
its use in the production of Plaster of Paris, and as Potters' stone,
because so much is sent to the Potteries for use in the formation of
moulds. Crystallized gypsum contains about 21 per cent, of com-
bined water, and when properly calcined for plaster about three-
fourths of this water is expelled. If the mineral be totally dehy-
drated it is spoilt, and the plaster is said to be " over burnt." A
Case on the western side of the Hall, near the window, illustrates
rather fully the manufacture and uses of Plaster of Paris.

Cavities occasionally occur in the masses of Triassic alabaster,
and on the walls of these cavities the gypsum often occurs in
beautiful crystals. The crystallized gypsum is known as Selenite,
a name said to refer to the pearly sheen seen on the cleavage-
planes, thought to be suggestive of moonshine, j A large series of
crystals of selenite will be found here, including some very fine
examples from the Kimeridge clay of Headington, near Oxford.
The crystals belong to the monoclinic system, and exhibit perfect

* " The Gypsum Deposits of Nottinghamshire and Derbyshire," by A. T.
Metcalfe. Trans. Fed. Inst., vol. xii. (1896) p. 107 ; Rep. Brit. Ass. for 1893,
p. 760; Forty-second Ann. Rep. Soft. Kat. Soc, 1895, p. 19.

t Although selenite .derives its name from aiXrtvr) (selene) the moon, the
mineral must not be confounded with the "moonstone" of the jeweller,
which is adularian felspar. See specimens in Horse-shoe Case, Section T.

18 1 MINERALS OF THE NEOZOkh sto.ata

cleavage parallel to the clinopinacoid. Many of the crystals are
of tabular habit, and the large lozenge-shaped face seen on several
of the specimens is this plane of easy cleavage. Thin transparent
cleavage-flakes, mostly of diamond shape, were formerly used to
a limited extent in place of glass. The mineral may be cleaved
also, though less perfectly, in two other directions.

Twin crystals are common in gypsum, as seen in Nos. 1393, 1394 ;
and the twinning may give rise to arrow-headed and swallow-tailed
crystals. The faces are often curved, as in No. 1395, whilst in some
instances the crystals become quite lenticular in shape, as in
No. 1396. The specimen No. 1399 is a group of lenticular crystals
from the Oldhaven beds of Reculver Cliff, in N. Kent, remarkable for
having a large proportion of sand mechanically associated with the
gypsum — an occurrence which reminds the mineralogist of the so-
called " Fontainebleau sandstone," in which calcite mixed with much
sand has crystallised in rhombohedra. (See specimens in Horse-
shoe Case, Section I.)

Crystals of selenite, often known in brickyards as "congealed
water," are common in most clays arid in many shales, which
are simply indurated and laminated clays. The mineral may
be formed in such situations by the action of sulphuric acid or of
sulphate of iron, resulting in either case from the decomposition of
iron pyrites, on calcareous matter, such as that of shells. In lime-
stone a similar reaction may occur. Crystals of gypsum have been
formed artificially by allowing a solution of ferrous sulphate, in con-
tact with air, to react on chalk, the gypsum being here accompanied
by the formation of ferric hydrate. Such an association, brought
about naturally, is illustrated by a specimen from Brighton in the
Horse-shoe Case.

Examples of selenite are exhibited not only from the Keuper marl
and from the Kimeridge clay, as mentioned above, but also from the
Woolwich and Reading clays, as in No. 1398, presented by Dr.
G. Abbott. The late Professor P. M. Duncan, in calling attention
to the occurrence of moulds in certain Eocene clays, indicating the
former presence of selenite, explained the removal of the mineral
by assuming that deoxidation had been effected by means of de-
composing organic matter, whereby the sulphate had been reduced
to sulphide of calcium, which is an extremely unstable substance.*
Professor Lacroix has remarked that if calcium sulphide be acted
on by a solution of acid carbonate of iron, the products of the
reaction may be pyrites and calcite.f Gypsum may be readily
removed from one spot and carried to another by mere solution
in water. According to Mr. G. K. Cameron, one part of gypsum is
soluble in 372 parts of pure water at 26°C. It is well known that

* " On the spaces formerly occupied by Selenite in the Lower Eocene Clays
of the London Basin ; with Remarks on the Origin and Disappearance of the
Mineral." Quait. Jouni. Geol. Soc., vol. xxii. (1866), p. 12.

f " Le Gypse de Paris." Xouv. Archiv. Mus. d'Hist. Nat., 3 ser.. vol. ix.
(1897) p., 201. : ^

A^fffrDRITE, ETC. 185

Waters draining gypseous rocks, like those of the Trent, contain
much sulphate of lime in solution; and such permanently hard
waters, valued for brewing as at Burton, are said to be " selenitic."

The decomposition of gypsum gives rise in some cases to the
elimination of Native Sulphur, as shown in a specimen in the Hall,
where sulphur is seen in a mass of gypsum from Newark. Mr. R.
P. Cafferata has remarked that in the course of twenty-four hours
after quarrying the " Blue Rock " free sulphur appears in consider-
able quantity.* The reduction is generally effected by organic
matter, probably through the agency of sulphur bacteria.^

Gypsum is readily converted into calcite, even in the cold, by the
action of a solution of certain carbonates. A crystal of gvp.sum
which has undergone this change will be found in the interesting
group of artificial pseudomorphs, prepared and presented many
years ago by Dr. H. C. Sorby, F.R.S., and exhibited in Wall Case '■'> 5.

According to official statistics the amount of gypsum raised in
England in 1902 was 224,669 tons. This amount was yielded by the
following counties, the first-named being the largest producer, and
the others in regular sequence yielding less and less : Nottingham,
Stafford, Cumberland, Sussex, Derby, Yorks, Westmorland and
Somerset. Whilst most of the gypsum comes from the Keuper marl,
it has been pointed out by Mr. J. G. Goodchild that the gypsum of
Edenside is referable to a lower horizon, being on or near the Mag-
nesian Limestone. J

Widely different in geological age, from the Permo-triassic
gypsum, is the gypsum of Sussex, of which a sample is here shown
(Xo. 1385). This mineral was discovered in the famous sub-Wealden
boring at Mountfield, near Xetherfield, not far from Battle, and is
believed to be of Purbeck age. Much gypsum occurs in the Isle of
Purbeck, and the mineral was formerly worked in the lower Purbeck
beds of Durlston Bay.§

Anhydrite (No. 1400.)

Whilst gypsum contains two molecules of water of crystallisation,
the mineral called Anhydrite is a sulphate of calcium destitute of
water, whence indeed its name. Unlike gypsum, anhydrite crystal-
lises in the orthorhombic system, but crystals are rare, at least in
this country. Anhydrite is harder and denser than gypsum, and
admits of being polished like a piece of marble. It frequently
presents a pale blue colour, as seen in Xo. 1400.

Anhydrite readily passes into gypsum, with an increment of volume
of about 60 per cent., and conversely gypsum may become converted
into anhydrite. It has been suggested that much of the gypsum in

* Cited by Mr. Metcalfe, op. cit.

f Prof. Lacroix : " Mineralogie de la France," vol. ii (1897), p. 370.

* " Some Observations upon the ^Natural History of Gypsum," Proc. Geol.
Assoc., vol. x (18*8), p. 425.

§ "The Geology of the Isle of Purbeck.' - By Aubrey Strahan, M.A.
Mem. Geol. Surv., 1898, p. 237

7882 O

- 8(1 MINERALS OF T*UE NEOZOIC STRATA,

this countrymay have been derived from the alteration of anhydrite.
In Nottinghamshire anhydrite occurs in the heart of certain masses
of gypsum, and this kernel seems to represent the original mineral.
It was formerly supposed that the production of anhydrite required
a moderately elevated temperature, but it is now known that the
mineral may be deposited at normal temperature, especially from
saline solutions. The researches of Professor van't HofE have shown
that " solutions containing, calcium sulphate which have a tension
lower than 17 . 2 m.m. at 25° deposit it as anhydrite. This is the
case in the deposition from sea-water."*

Celestite (Nos. 1401, 1402.)

Native sulphate of strontium, like sulphate of calcium, is a mineral
not infrequently found in the New Red Sandstone. Its occurrence
in the Bristol district has already been described (p. 113) and some
fine examples are exhibited in Case VII., but a specimen is also placed
here, in order to illustrate with some approach to fulness the
mineral products of the Trias (No. 1401).

Cdestite, or cdestine, is frequently found in association with gyp-
sum, as illustrated by No. 1402 and by specimens in Section G of the
Horse-shoe Case. Even when not detected by the naked eye the
presence of celestite in gypsum may sometimes be revealed by the
microscope. Natural waters, especially in the New Red Sandstone,
often contain an appreciable quantity of sulphate of strontium. Its
occurrence in the water of the famous dropping well of Knares-
boroughj and in the Bristol waters has already been referred to
(p. 114).

Celestite is found in many sedimentary strata, though by no
means so common a mineral as barytes. A specimen in the Case
illustrating Fossilisation is interesting as showing celestite finely
crystallised in the chambers of an ammonite from the Lias of
Adderley in Shropshire.

Collectors of minerals are familiar with the flints of Meudon, near
Paris, containing crystals of celestite, of which a specimen will be
found in the Horse-shoe Case, but the mineral is not known to occur
in the chalk -flints of this country.

Banjtes (Nos. 1403 to 1406).

Barium is an element of much wider diffusion than the kindred
element strontium, occurring as it does in a large number of rocks,
both sedimentary and eruptive, and in many natural waters.J
Attention has been called in recent years to the occurrence of barium
in many of the Triassic sandstones. Mr. A. Strahan, in describing
the rock of Beeston Castle in Cheshire, which is Keuper sandstone,

* Journ. Chem. Soc, vol. lxxxii (1902), Part ii., p. 138 : abstract of paper
by van't HofE and Weigert in SUzungsber. K. Akad. Wiss. Berlin, 1901.
•(• Proc Yorkshire Oeol. and Polyt. Soc., new ser., vol. xiii., p. 135,
J See Delkeskamp's paper cited on p. 169.

BARYTES, 187

alluded to the veins of Barytes in the joints of the rock, and to the
occurrence of the mineral in the rock itself, as well as in the breccias
of the Peckforton Hills.* Prof. Clowes found barium
sulphate in the Bunter sandstone of the so-called " Hemlock Stone,"
near Nottingham, where it occurs as a cementing medium uniting
the siliceous grains.t Prof. W. W. Watts has described the
occurrence of barytes under similar conditions in the Lower Keuper
sandstone of Peakstones Rock, near Alton, in Staffordshire. % So
again, the occurrence of barytes in both Bunter and Keuper sand-
stone at Bidston, in Cheshire, has been recorded by Mr. C. C. Moore
and Mr. J. Lomas.§ It should be noted too that Dr. H. T. Brown
has found barium existing in the form of carbonate in some of the
Triassic sandstones in Cheshire, whilst Professor Clowes has sug-
gested that the reaction of this soluble compound with certain
sulphates may have led to the formation of barytes in the rocks.
Gypsum is not uncommon in the sandstones of Nottinghamshire.

In mineral waters barium frequently exists in the form of chloride.
An exceptionally large proportion was found by Prof. E. T.
Thorpe in the waters of Harrogate, the water of the Montpellier
Strong Sulphur Well yielding an amount of barium equivalent
to 9-5 grains of chloride per gallon.|| It is notable, too, that the
proportion of barium in the Harrogate water seems to be increasing.
Barium chloride also occurs, to the extent of more than 6 grains
per gallon in the waters of Llangammarch Wells in Breconshire.

As far back as 1847 Dr. Richardson detected barium in the waters
of Walker Colliery, near Newcastle, and a large mass of barytes
was found in Felling Colliery.^} Prof. Clowes has called atten-
tion to the large proportion of barium in the waters of certain col-
lieries in Durham, which is the cause of a deposit forming in the
pipes and water boxes connected with the mining pumps. In
some cases the deposit contains as much as 90 per cent, of sulphate
of barium, and it is an interesting fact that sulphate of strontium
is also present in the deposit, in some cases to the extent of 8 per
cent. Prof. Bedson found barium chloride in the colliery
waters, and, as Prof Clowes remarks, this solution would give
rise to a precipitate of barytes by reaction with ferrous sulphate,
or with free sulphuric acid, which might readily result from the
decomposition of pyrites. In Case VIII. will be found a nodule
of clay ironstone enclosing barytes, from the Whitehaven coal-field
(No. 1091), and it is known that barytes like wise occurs in the Coal-
brook Dale ironstone.

* "The Geology of the Neigh bourhood of Chester." Mem. Qeol. Surv.
Expl. Quart. Sheet 80, S.W. 1882.

t " Barium Sulphate as a Cement in Sandstone." Proc. Roy. Soc, vol.
xlvi. (1890), p. 363.

% Rep. Brit. Assoc, for 1894, p. 065. Qeol. Mag., [iv.] vol. i. (189-4), p. 520.

§Proc Liverpool Qeol. Soc, vol. viii. (1900), p. 241.

|| Journ. Chem. Soc., vol. xxxix. (1881), p. 510

^f " On Minerals and Salts found in Coal-pits.' • By R. Calvert Clapham
and John Daglish. Trans. N. Eng. Inst. Min. Eng., vol. xiii. (1864), p. 219.
7882. o 2

18S MINERALS OF THE NEOZOIC) STRAtf A.

In the Triassic sandstone of Elgin barytes has been found, and
here Dr. W. Mackie regards it as a precipitate from an inland sheet
of salt water.* Commander A. Carpenter dredged off Colombo,
in the Indian Ocean, in 675 fathoms of water, small nodules con-
taining 75 per cent, of barium sulphate.f

It is worth noting that certain crystals of barytes from Teplitz,
described by Dr. F. Becke, appear to have been formed by pre-
cipitation from the hot springs, where, though the crystals reach
a length of five centimetres, the proportion of barium in the water
is so small as to elude analytical determination. J

The finest specimens of barytes yielded by the Neozoic strata
of Britain are the large yellow crystals formerly found rather abun-
dantly, though now rare, in the pits worked for fuller's earth in the
Lower Greensand of Nutfield, near Redhill, in Surrey (Nos. 1403-
1404). As far back as 1819 this occurrence was described by
Thomas Webster, who speaks of masses of barytes found here weigh-
ing a hundredweight^ The crystals, which though large are rarely
terminated, were studied by Prof. Chapman, of University
College, London, who described the mineral as barytine.\\ Some
excellent examples of the Nutfield barytes are here shown, and
others will be found in the Horse-shoe Case. The crystals, rather
like sugar-candy in colour, are associated with crystallised quartz,
sometimes slightly amethystine in tint. Iron-pyrites also occurs
with the barytes, and a little carbonate of copper has occasionally
been found. The presence of barytes was not favourably viewed by
those who worked the fuller's earth.

Very different from the Nutfield mineral is the barytes occasion-
ally found in the septaria of the London clay, especially in the
Isle of Shepf ey. Here it occurs in slender opaque white crystals,
arranged in radiating forms or in stellate groups, and rather effec-
tively disposed on the yellow calcite which has crystallised in the
contraction-cracks of the nodules, and was formerly called the
" waxen vein." This occurrence of barytes was recognised by such
early observers as Dr. Grew and Sir John Hill, who described the
mineral under the name of lepastrum, and appear to have regarded
it as gypsum. Some of the specimens here shown (Nos. 1405,
1406) are said to have come from Whitstable Bay ; and according
to Sowerby the barytes was also found under similar conditions at
Southend, at Sydenham, and at Highgate.^j

Prom the difficulty of dissolving sulphate of barium, it might be
supposed that the mineral would be extremely immobile, not easily
removed from one place and deposited in another. According

* Rep. Brit. Assoc, Glasgow, 1900, p. 649.

f Journ. Asiatic Soc. Bengal, vol. Ivi. (1887), p. 209. Quoted in " Report of
the Challenger."

% Tschermak's Min. Mit., vol. v. (1888), p. 82.

§ " On the Geognostical Situation of the Reygate Stone and of the Fuller's
Earth at Nutfield." Trans. Oeol. Soc, vol. v. (1819), p. 326.

|| " Mineralogical Notes," Phil. Mag. [4], vol. iii. (1852), p. 144.

^1 " British Mineralogy," vol. iii., p. 199 ; vol. v., p. 39.

COPPER-ORES. 189

to Holleman, one part of the salt requires for solution 420,700 parts
of water at 18.4° C* Referring to the waters of Bath, the Hon.
R. J. Strutt observes that " Barium sulphate requires half a milli on
times its weight of water to dissolve it ; radium sulphate perhaps
several hundred million times its own weight."f

Barytes not infrequently contains a small proportion of the
sulphates of strontium and calcium. With celestite the barvtes
is clearly isomorphous, but such relationship can hardly be extended
to the corresponding calcium salt, for though anhydrite crystallises
like the others, in the orthorhombic system, it yet differs markedly
in form and in cleavage.

Copper-Ores, etc. (Nos. 1407 to 110*).

Copper is rather widely distributed through many sedimentary
rocks, but is rarely present in large proportion, except in rocks of
the Xew Red Sandstone period. Dieulafait referred the origin of
the copper to deposition from sea-water. In the waters of the
Mediterranean, he found copper to the extent of - 01 gramme per
cubic metre ; and he showed that the black mud left by evaporation
of sea-water, whether in natural or in artificial basins, invariably
contained this metal.

Perhaps the most important copper-bearing rock of sedimentary
origin is the famous Kupferschiefer or copper-shale, of Germany,
which though only a thin stratum containing but 2 or 3 per cent.
of copper, has nevertheless been worked for at least seven centuries,
and still yields a large output of copper. The black shale is rich in
fossil fishes, like Palceoniscus, and it was suggested by Groddeck
that the discharge of cupriferous springs into the basin in which
the mud was in course of deposition must have destroyed the
fish-life, whilst the decaying organic matter would lead to the forma-
tion of sulphides. According to Dieulafait the copper might be
derived simply from sea-water, by evaporation in a closed basin ;
the gypsum which would be deposited in the lagoon might suffer
reduction by decomposing organic bodies, with the formation of
sulphides, which would precipitate the copper, in a sulphuretted
form. It is notable, however, that the marl-slate of Durham,
which is a Permian deposit at the base of the Magnesian Limestone,
on precisely the same horizon as the German copper-shale and
closely related to it palaeontologically, appears to be quite destitute

of copper. J

The copper-bearing strata of this country are almost exclusively
of Triassic age. Reference has already been made to the occurrence
of copper-ores in the Dolomitic Conglomerate of the West of

* Zeit. Phys. Chem., vol. xii., p. 125.
t Proc. Roy. Soe., vol. lxxiii. (1904), p. 195.

1 See Prof. Lebour's remarks in Trans. Inst Mining En",., vol. xxiv. (1904),
p. 390.

190 MINERALS OE THE NEOZC 7 . 7.™._:'

England (p. 112), but the most noteworthy examples of cupriferous
strata are to be found in Cheshire, where sandstones and conglo-
merates, formerly regarded as Keuper but now referred by some
authorities to the Bunter, have been systematically worked for
copper at Alderley Edge and at Mottram St. Andrews, near Maccles-
field, the beds being there repeated by a fault. The bright colour
of the copper carbonates in these rocks propably attracted attention
at a very early period ; and the rude stone hammers found by Prof.
Boyd Dawkins, Dr. Sainter, Mr. Roeder, and others, point to work-
ings even in prehistoric times.*

At Mottram St. Andrews the copper was worked chiefly in a hard
quartzose conglomerate, which contained an average of about 5 per
cent, of copper-ore. At Alderley Edge, about a mile to the south-
west, the ores were mostly found in three beds of sandstone, where
the proportion of copper averaged about 1"4 per cent, of the work-
able parts of the stone. f The grains of quartz in the sandstone were
invested by a coating of copper carbonate. The specimen here
exhibited (No. 1407) is a quartzose conglomerate, with malachite
and azurite. The sandstones are variously coloured by several
mineral pigments — yellow and brown by iron oxides, blue and
green by copper carbonates, and black by manganese oxide and
earthy cobalt-ore.

Although these cupriferous sandstones are no longer worked, they
were at one time the object of rather extensive mining operations, and
the ore was profitably treated by a wet process. The coarsely ground
sandstone was digested with dilute hydrochloric acid, whereby the
copper was dissolved out, and from this solution of the chloride
the metal was precipitated by scrap-iron. The " cement copper " con-
tained about 80 per cent, of metallic copper. The cobalt, which
occurred to a small extent in the sandstone in the form of asbolan,
was recovered by adding milk of lime to the liquor after removal of
the copper. The precipitate thus obtained carried the cobalt, with
a little arsenic. It is notable that copper is also accompained by
cobalt in many other localities, as at Bieber in Hesse.

Some of the Chesire sandstones contained also lead ore, chiefly in
the form of cerussite, though they likewise yielded subordinately
galena, pyromorphite and vanadinite. A sample of Alderley Edge
sandstone, with lead-ore is here exhibited as No. 1408. Attempts
to treat the plumbiferous sandstones were not commercially
successful. These stratified lead-ores rather remind the miner of
the sandstones which are extensively worked near Mecbernicb and
Commern, in Rhenish Prussia, where the Bunter sandstone contains
nodules, or Knotten, of galena, associated with cerussite and locally
with a little c6pper carbonate.

* " Prehistoric and subsequent Mining at Alderley Edge," by Charles
Roeder. Trans. Lancashire and Cheshire Antiq. Soc, vol. xix. (1902).

\ Mem. Oeol. Surv. Prof. Hull's Memoir on Geology of Stockport. Also
Mr. Greenwell in Proc. S. Wales Inst. Min. Eng., vol. iv. (1866), p. 44.

j^i -ui\do.

191

Sir H. E. Roscoe many years ago described a vanadate of lead and
copper, which was found at Alderley Edge and at Mottram St.
Andrews, to which he gave the name of Mottramite. It formed on the
sandstone a thin incrustation, in some cases black and velvety, with
crystalline structure, and in other cases compact and of purplish
brown colour.*

It may not be without interest to recall the fact that other vana-
dates are elsewhere present with Permian copper-ores ; witness
the occurrence of volborthite, a vanadate of copper, in the cupriferous
sandstone of Perm in Russia.

Iron-ores (Xos. 1409 to 1419).

Of the many iron-ores found in the Secondary strata of Britain
the most famous is the ore of the Cleveland district in the North-
east of Yorkshire (No. 140'.i). The Cleveland ore occurs in the Middle
Lias, or Marlstone, where it forms several bands, the most important
seam being nearly twenty feet in thickness. Though not everywhere
uniform in character, the ore when freshly raised is typically a light
bluish-green oolitic rock, containing about 30 to 32 per cent, of iron,
chiefly in the form of carbonate.f The greenish colour is referred to
the presence of glauconite, or some other silicate of iron, whilst the
bluish tint may be due to a phosphate like vivianite. Phosphorus is
always present, though in variable proportion, the average being
about 1 -j per cent. As the ore is highly fossiliferous the origin of the
phosphorus is readily traced. Indeed the two principal beds of ore
are known, from their characteristic fossils, as the Pecien Seam and
the Avicula Seam. Traces of various extraneous metals, like zinc,
nickel, and cobalt, are commonly present in the Cleveland ore ; and
Mr. A. Dick, in the course of an analysis found in the insoluble
residue, microscopic crystals of Anatase, associated with quartz. J
Titanium oxide, in the form of anatase and of rutile, has been shown
by several recent observers to be widely distributed in the sedimen-
tary rocks of this country. $ The presence of zinc in the Cleveland
ore offers no difficulty, inasmuch as the frequent association of

* "On two new Vanadium Minerals." Proc. Boy. Soc, vol. xxv. (JSTC),
p. ILL The other mineral referred to in the title of the paper is the vanadiuru-
mica called Boscoelite (p. 109).

f For full description of the Cleveland ore, see Merits. Geol. Sun: " The
Geology of North Cleveland," by George Barrow, ls.sj, p. SO. " The Jurassic
Rocks of Britain, vol. i., Yorkshire." by C. Fox-Strangways, 1892, p. 433.

% " The Iron-ores of Great Britain," (Mem. Geol. Sun:), part i., p. 95.

§ See Mr. Scrivenor's paper on " Anatase in the Trias of the Midlands of
England," in Min. Mag., vol. xiii. (1903), p. :548, where references are given
to the work of Dr. J. H. H. Teall, Mr. Maynard Hutchings, Mr. A. Dick, and
Mr. H. H. Thomas. In a paper on the " Distribution of Titanic Oxide upon the
Face of the Earth" (Am. Jo»rn. Sc. [3], vol. xlii., 1891, p. 491), Prof. F. P.
Dunnington records his examination of " black garden soil from Kensington,"
which yielded 0-21 per cent, of titanic oxide. The common occurrence of
titanium in iron-ores explains the origin of the eyano-nitride of titanium,
which is occasionally found in small copper-like cubes in the " bear " of
blast furnaces.

192 MINERALS OF THE NEOZOIC STRATA.

zinc-blende with carbonate of iron is well known, and is very
marked in the Lias.* According to Professor Hartley tbe Cleveland
ore, like many other ores of iron, contains gallium.

From the microscopic structure of the Cleveland iron-ore, Dr.
Sorby showed, many years ago, that it had probably been originally
an oolitic limestone, which became altered by the action of a solution
of bicarbonate of iron, derived perhaps from the interstratified shales
which contained oxide of iron and organic matter. f In some of the
fossil shells associated with the ore, the carbonate of lime is partially
replaced by ferrous carbonate.

The Cleveland ore is raised at the present time (1904) to the extent
of about 5,600,000 tons per annum,an amount which represents rather
more than two-fifths of the total output of iron ore in the United
Kingdom. The iron-ores of the Middle Lias have been worked not
only in Yorkshire, but also in Lincolnshire, Leicestershire, and
Oxfordshire. The ore of Frodingham in N. W. Lincolnshire is refer-
able, however, to the Lower Lias.J:

At Rosedale Abbey, in Yorkshire, there occurs an oolitic
ironstone of nearly black colour, peculiar in being magnetic and
polar. This magnetic iron-ore represented by No. 1410, occurs in
the Dogger series, belonging to the Inferior Oolite. Crystals of
magnetite, as Prof. Lacroix has pointed out, occur in some of the
oolitic brown iron-ores of France. The formation of magnetite in
the wet way possibly receives illustration from an observation of
F. M. Stapff, who found that the rust on nails from ancient mines
in Spain, believed to be 2,000 years old, consisted of a mixture of
limonite and magnetite. §

Prof. Bauerman has called attention to the similarity of the
Rosedale ore to the mineral worked on the Continent under the
name of Chamoisite — a pisolitic magnetic ore of Jurassic age.||

A vast quantity of siliceous brown iron ore is raised annually from
the Oolites of this country.^ The Northamptonshire ore (No. 141 1 )
largely developed in the Northampton sand, forming part of the
Inferior Oolite, presents the aspect of a rusty brown granular mass,
composed of iron hydroxide and quartz. At considerable depths,
however, the unaltered ore is a bluish or greenish grey substance,

* See for instance, " The Yorkshire Lias," by Ralph Tato and J. F. Blake,
1876, p. 163. Also Mr. C. Fox-Strangways' Geol. Surv. Mem. on the Jurassic
Rocks of Britain, vol. i., p. 473.

f " Origin of the Cleveland Ironstone." Proc. Geol. Polytech. Soc. West
Riding, vol. iii. (1856-7), p. 460. Also : Quart. Journ. Geol. Soc, 1879.

| See paper by the late Rev. J. E. Cross in Quart. Journ. Geol. Soc, vol. xxxi.
(1875), p. 115. Also, Mem. Geol. Surv. " The Jurassic Rocks," vol. iii.
By Horace B. Woodward, 1893., p. 300.
, § Jahrb. f. Min., 1895, part i., p. 69.
£, || " A Treaties on the Metallurgy of Iron, 6 ed., 1890, p. 87.

If It may be not°d that the Jurassic brown ores of Luxemburg and
Lorraine are known as minette — a diminutive of mine, or ore. Iron-ore is
often called in this country "min"," and the diminutive would indicats a
lean or poor ore. Minette is used also as the name of an igneous rock.

IKUJN-UKES.

193

composed mainly of impure ferrous carbonate. The bluish colour
is regarded by Professor Judd, as probably due to the diffusion of a
small proportion of iron sulphide throughout the mass, whilst the
greenish tint may be referable to the presence of ferrous phosphate
rather than to a silicate.*

The brown iron ore of Westbury, in AViltshire (No. 1413), and
that of Abbotsburv, in Dorsetshire, are referable to the Corallian
strata. At a slightly higher horizon is the brown iron ore, which
was found in the Dover boring. This ore forms a band 12 feet
in thickness, described by Prof. Boyd Dawkins as composed of
grains of hydrated oxide of iron in a base consisting partly of
carbonate of lime and partly of carbonate of iron.f The ore
of Seend, near Devizes, in Wiltshire, occurs in the Lower
Greensand ; indeed much of this Greensand consists of iron-
shot sands, and the proportion of iron occasionally rises
sufficiently high to constitute a siliceous iron-ore. Examples of all
the Jurassic and Cretaceous iron-ores are shown in the Wall cases
47 and 49, and others will be found in the Petrographical
Collection.

Ironstone was formerly worked on rather a large scale in the
Wealden beds, principally in the AVadhurst clay, but also to a limited
extent in the Ashdown sands. The ore (No. 1414) is a kind of
clay ironstone, containing as much as 35 per cent, of metallic iron.
It was this ore that formed the raw material of the iron industry
which flourished for ages in the Weald of Sussex and Kent, and was
not extinguished until the early years of the nineteenth century.
Many of the "bell pits" from which the ore was raised still exist,
though now generally filled with water. The ore was smelted with
charcoal as a fuel — the charcoal being mainly derived from the oak
forests on the Weald clay — and with the Paludi'.ta (Viviparus)
limestone, or Sussex marble, as a flux. Cinder-heaps, or accumula-
tions of old iron-slags, still exist in the Weald. J

In the Tertiary strata nodules of clay ironstone have occasionally
been worked, as at Hengistbury Head in Dorsetshire, where the ore
occurs in the Barton beds. The bog ores show the formation of iron-
ore in progress at the present day, and may throw light upon the
origin of some of the brown iron-ores of the sedimentary rocks. Mr.
Hudleston has called attention to the fact that iron in rocks is
rendered locomotive by means of carbonic acid, a soluble acid
carbonate being formed, and is fixed by means of oxygen, the solution
of bicarbonate on exposure to air depositing the hydroxide as a kind
of bog ore.§

*Mem. Geol. Surv. " Oology of Rutland," 1875. By John W. Judd.
p. 110. " Jurassic Rocks." vol. iv. By Horace JB. Woodward, p. 493.

t Trans. Manch. Geol. Soc, vol. xxii. (1895), p. 501.

% Mem. Geol. Surv. " The Geology of the Weald." By William Topley
1875, p. 329.

§ " On the Geological History of Irou-ores." Proc. Geol. Assoc, vol. xi.,
( 1889), p. 104.

194: MINERALS OF THE NEOZOT.

Organic agencies probably play a great part in the formation
of deposits of bog iron-ore. The Rev. Dr. A. Irving has called
attention to the importance of organic acids in the solution, the
transport and the deposition of iron-ores.*

It is known, too, that ferrous salts may be oxidised to the
ferric state, without exposure to air, by the aid of ferro-bacteria.
On the other hand, organic action may reduce the ferric hydroxide to
the ferrous condition, and then, by means of carbonated water, a
soluble bicarbonate may be formed. Kindler observed, as far back
as 1835, that where pine trees were planted in sand-hills, the iron-
shot sands became rapidly decolourised in the neighbourhood of the
decaying roots.

Ferric hydrate has great agglutinating power, and masses of sand
and gravel cemented by deposits of this substance are very common
where chalybeate waters percolate through beds of loose material,
forming what is known as " fan." By the filtration of meteoric
water through ferruginous sands curious concretionary forms may be
produced — tubular, globular, box-like, or quite irregular and cap-
ricious in shape (No. 1415). Some of the specimens from the Lower
Greensand of Leighton Buzzard (Nos. 1416, 1417) look like rusty
cannon balls, but they are often mere shells, and one of them broken
open here displays the hollow interior. The nodules may enclose
sand, or other substances, which rattle when the nodule is shaken.
Such concretions were formerly called Eagle stones — a name applied
also to other hollow stones, such as chalk flints, with loose matter
in the interior. The most extraordinary virtues were formerly
attributed to these nodules.f No. 1418 is an old specimen of an
"eagle stone," or Mtites, mounted in silver, as an amulet, but
this may not be British. That such ferruginous concretions may
be of comparatively recent origin is shown by the discovery in
Dordogne, some years ago, of what was described as a geode of
hydrate of iron containing 200 silver coins of the sixteenth or seven-
teenth century-!

Limonite, or brown iron ore, occurs not infrequently in stalactitic
forms, which, when broken transversely, show a radial structure, the
fibres being arranged in a direction normal to the axis of the stalac-
tite. The surface is often lustrous, and this is specially notable
in those varieties which contain manganese. Most bog iron-
ore contains manganese in greater or less proportion. E xamples of
the rapid formation of stalactitic limonite are often to be observed
in the deserted levels of old mines. Thus, Mr. Postlethwaite records
a case in which the Woodend Mine, near Threlkeld, was re-opened
after having been closed for thirteen years, and stalactitic and other

* " Organic Matter as a Geological Agent." Proc. Geol. Assoc, vol. xii.
(1892), p. 2'27. H: e also on the Humus Acids, Prof. Julien, in Proc.
Am. Assoc. Adv. Sc, vol. xxviii. (1879), p. 311.

f " A Lapidary : or the> History of Precious Stones." By Thomas Nicolf,
Cambridge, 1652, p. 148. " The Natural History, Ancient and Modern, of
Precious Stones and Gems." Bj C. W. Kirg, M.A., 1865, p. 49.

X M. Marrot in Butt. Soc. Geol. Fr., ser. ii., vol. iii. (1846), p. 527.

195

deposits of limonite filled up more than half the width of the level *
The recent formation of stalactitic limonite is illustrated by
No. 1419 — a specimen from a shaft in the camp at Dolbury, near
Churchill in Somersetshire.

It should be observed that certain kinds of brown iron- ore, bog-
ore and ochre contain a larger proportion of water than exists in true
limonite, and they should consequently be referred mineralogically
to the species called Limnitc or xanthosiderite . The term StUpno-
siderite is sometimes applied to limonite which presents a pitchy
black surface, generally connected, as remarked above, with the
presence of manganese. The surface of bog iron-ore often appears
scoriaceous, and may present a brilliant iridescence.

Glauconite (Xo. 1120).

Many sedimentary rocks, especially sandstones, are speckled with
dark green grains of the mineral called Glaucoit He. This is essentially
a silicate of iron and potassium, but presents such a variability of
composition as to suggest that it is a mixture rather than a true
species. The specimen Xo. 1420, representing the green colouring
matter of certain beds of Lower Greensand at Compton Bay in the
Isle of Wight, was examined microscopically by Dr. Teall and
analysed by Mr. Hort Player, who found that it yielded 9 ■ per cent.
of alumina, f

The grains of glauconite are usually the internal casts of the
chambers of foraminifera, or are otherwise connected with organic
structures. The mineral may have been derived from the alteration
of pyrites or of certain ferro-magnesian silicates. By meteoric
influences it may become converted into ferric hydrate, and hence
many sandstones which are green where unexposed become rusty at
the outcrop.

It is noteworthy that the green sands and muds found by the
" Challenger " in shallow water, along Continental shores, are cha-
racterised by the presence, more or less abundantly, of glauconitic
grains and casts, associated with green amorphous matter, probably,
at least in part, of organic nature. Glauconite is also present, though
in smaller proportion, in the blue muds. It is most abundant near
the " mud line" surrounding Continental shores, that is, at about the
lower limit of the action of waves, tides and currents. *

With regard to the origin of the glauconite, it has been suggested
that the mud which gained access to the interior of a shell or test mio-ht
contain iron sulphide which became oxidised, and the sulphuric acid
resulting from this alteration would form by acting on the clay
aluminium sulphate with elimination of colloidal silica, which in a
nascent state might combine with the oxide of iron in the mud. As

* " Mineral Springs near Keswick," Trans. Cumberland and West. Assoc,
No. 11.

■\Mern. Geol. Surv. " Geology of the Isle of Wight." 2nd ed., 1889, p. 255.
J " Challenger '1 Report, " Deep Sea Deposits." 1891. p. 378.

196 MINERALS OF THE NEOZ

UiL OliUllA,

to the potash, it seems to have been derived from the sea-water
itself, and probably owed its original source to the orthoclase and
mica of the detrital matter.*

Pyrite (Nos. 1421 to 1424).

Whilst certain rocks of subaqueous formation present a greenish
colour which they owe to disseminated grains of glauconite, other
sedimentary rocks — especially certain clay3 like the gault — are
characterised by a dull bluish colour which has been referred to the
presence of finely divided iron-pyrites. f In most eruptive rocks,
Pyrite may be regarded as an original constituent, but in other rocks it
occurs as a secondary product, formed generally by the alteration
of various ferro-magnesian minerals.

In sedimentary strata the pyrites often owes its immediate origin
to the reduction of a solution of ferrous sulphate, but this salt itself
usually results from the oxidation of pyrites, so that the changes
follow in a cycle. The reduction of the sulphate of iron by organic
matter explains the common occurrence of pyrites in fossil shells,
lignite and other organic structures. Instances of the recent forma-
tion of pyrites by decomposing organic matter are very familiar, one
of the best being the case recorded by Pepys in which it resulted
from the decayed bodies of mice which had fallen into a vessel con-
taining a solution of ferrous sulphate. %

Iron existing in solution as a carbonate, in water containing car-
bonic acid, may be converted into pyrites if sulphates and certain
deoxidising agents be present. Thus, sulphate of lime in natural
waters may be reduced by organic agencies, and the resulting
sulphide, acting on the iron carbonate, may give rise to sulphide of
iron. In other cases the sulphur may be supplied from organic
sources. In the Percy Collection in the Victoria and Albert Museum
there is a specimen (No. 3697) showing iron-pyrites in a log of wood
from the yacht " Osborne/' which had lain for a considerable t'me
in a pond at Portsmouth that received the discharge of two drains. §

Pyrite is one of the commonest minerals in the Neozoic strata,
occurring sometimes in cubic crystals, often in the form of nodules,
and very frequently in disseminated grains (Nos. 1421, 1422). By
early writers like Henckel, the German pyritologist, the crystallised

* On Glauconite see also von Giinibel's paper, " Uebtr die Natur und Bil-
dungsweise des Glaukonits." Sitzungsber. Akad. Miinchen, vol. xvi. (1886).
Math.-Phys. Kl., p. 417.

f Ebelmen, for instance, referred the bluish tint of certain Oolitic rocks to
finely-disseminated pyrites (Comptes renins, 22 Dec, 1851 ; Bull. Soc. Geol.
Fr. [2], vol. ix., pp. 213, 221). It should, however, be added that Mr. Maw
doubted the pigmental effect of pyrites. See his paper " On the disposition
of Iron in Variegated Strata," Quart. Journ. Geol. Soc, vol. xxiv. (1868).
p. 351.

t " Notice respecting the Decomposition of Sulphate of Iron by Animal
Matter." By W. H. Pepys. Trans. Geol. Soc, vol. i. (1811), p. 399.

§ Catalogue of the Percy Collection (H-92), p. 433.

iRON-p'srRiTEs. 197

pyrites was called " marcasite," or some variant of that word* ; but
the practice of modern mineralogists is to apply the term marcasite
to the orthorhombic species of iron disulphide, and to restr'ct the
name pyrite to the cubic species. The common term " iron-pyrites "
is often loosely used, in a general sense, to include both modifica-
tions of the mineral — a practice not without convenience, inas-
much as it is sometimes difficult, in the absence of crystalline form, to
determine to which species a given specimen belongs. It is true the
colour of marcasite is paler than that of pyrites, but the colour is
frequently deepened and disguised by tarnish. Density is said to
offer a criterion. According to Prof. Julien, who has made a special
study of pyrites, the specific gravity of normal marcasite is very near
4 " 8, whilst that of pure pyrite is approximately 5 • 01 ; but the density
is subject to much variation, since the pyrite may be associated with
marcasite in a state of intimate mechanical mixture, forming what
has been called " marcasitic pyrite. "f Some doubt, however, has
been thrown upon this observation by Mr. H. X. Stokes.

Whilst some kinds of pyrites are very stable, others are extremely
prone to decomposition. Two kinds of alteration are recognised.
In one case, sometimes called the hepatic change, a slow oxidation
occurs, whereby the pyrite becomes externally altered to limonite,
with perfect preservation of form. Examples of this limonitisation
have already been noticed in connection with such specimens as No.
428 (p. 01), and other pseudomorphs of brown iron oxide after
pyrite are shown here (No. 1423). Such an alteration may be brought
about either by the direct action of water containing oxygen or
indirectly by conversion first into a carbonate and subsequently to
hydroxide.

In the other kind of change, sometimes distinguished as the saline,
the sulphide is oxidised to ferrous sulphate, known as a mineral under
the name of inelanterite, with elimination of free sulphuric acid. The
melanterit ; itself may then suffer decomposition, forming basic
ferric sulphates, like copiapite and apatelite,% with further production
of sulphuric acid. It has been said that vitriolisation is more common
with marcasite than with normal pyrite ; and where pyrite suffers
such a change there is probably some admixture with marcasite. In
some of the pyritised fruits of the London clay of Sheppey examined
by Julien, the presence of distinct octahedra showed the existence of
true pyrite, but it was probably accompanied by marcasite. §

The so-called ' marcasite ' jewellery of the eighteenth century was
invariably true pyrite, the brilliant polished surface of the mineral

* " Pyritologia ; or a History of the Pyrites, the Principal Body in the
Mineral Kingdom." Translated frcm the German. London: 1757. p. 14.

■f " On the Variation of Decomposition of the Iron Pyrites, its Cause and its
Relation to Density." By Alexis A. Julien. Ann. X. Y. Acad., Sc, vol. iv.
(1888).

% "Sur les produits di decomposition des pyrites, &c." Par Jl. A.
Lacroix. Bull. Soc. Fr. Min., vol. xx. (1897), p. 288.

§ " The microscopical structure of the Iron Pyrites." Joum. N. York
Micro. Soc., May 7, 1886.

198 MINERALS OP THE NEOZOIC STRATA.

being remarkably stable. A string of crystals of pyrite, believed to
be from a British locality, is here shown (No. 1424). Such orna-
ments, being formerly regarded as possessing medicinal virtue,
were known as " Health stones " (Gesundheitsteine) and it was held
that as the wearer sickened, so the stone tarnished.

Marcasite (Nos. 1425, 1426).

Since Haidinger in 1845 applied the name Marcasite to the
orthorhombic species of iron disulphide and restricted the term
pyrite to its cubic isomer, as previously explained, the names have
been generally used by mineralogists in this sense. The origin of the
word marcasite, usually attributed to an Arab source, has been the
subject of much learned discussion.*

Some of the best known crystals of marcasite from the ssdimentary
strata of this country are the beautiful specimens from the Chalk
Marl, between Dover and Folkestone.! They are usually groups
of twin crystals of the spear-head type, supposed locally to be heads
of Roman weapons. J Some excellent examples, attached to the
matrix, are here exhibited (No. 1425). According to Prof. Hartley's
spectroscopic studies, the marcasite of Dover contains thallium and
nickel. §

The Chalk of the south-east of England likewise contains, especi-
ally in its lower zones, much marcasite in the form of nodules, some-
times spherical but often most capricious in shape, and displaying
when broken a fibro-radiate structure (No. 1426). The exterior is
often rusty, by limonitisation, but the freshly fractured surface
is brilliantly metallic and of pale yellow colour. According to
Mr. H. N. Stokes|| the colour of pure marcasite is tin white, and
Prof. Julien makes the same remark, but tarnish or admixture with
pyrite renders it brass-like. Exposure rapidly induces a yellow
tarnish, which may pass into a brown colour. The nodules, often
known locally as 'thunderbolts' and 'fairy -balls,' may enclose an
organic nucleus ; or a hollow may be left by disappearance of a
fossil, and in this cavity pulverulent sulphur sometimes occurs — a
substance set free by the disintegration of the molecule of iron
disulphide. Some observers have recorded microscopic organic
structure in the substance of the nodules. It has been pointed out
by Mr. Stokes that a fibrous structure affords no clue to the
species. " Fibrous pyrite appears to be much more common than
fibrous marcasite.."

Of all metallic sulphides, marcasite seems the most unstable, and
its instability is generally responsible for the decomposition which

* See, for example, Dr. Sadebeok's communication to the Neues Jahrb.
Min. (1878). p. 289. " Ueber den Namen ' Markasit '."

| " Remarks on the Chalk Cliffs in the neighbourhood of Dover." By
William Phillips. Trans. Geol. Soc, vol. v. (1821), p. 36.

% Prof. Miers's " Mineralogy," p. 330.

§ " The wide Dissemination of some of the Rarer Elements, etc."
Journ. Chem. Soc, vol. lxxi., part i. (1897), p. 533.

II Bull. U.S. Geol. Surv., No. 186, 1901.

QUARTZ. 199

pyritised structures frequently suffer. Several examples of fossils
mineralised with iron disulphide will be found in the Case
illustrating Fossilisation. The pyritic nodules, more or less
altered, occurring in the Gault of Cambridgeshire are known
locally as " rugg-s tones."*

Iron-pyrites, generally marcasite, was formerly used, like flint, for
eliciting sparks by impact with steel ; hence in old works there is
sometimes confusion between pyrites and flint, both substances
being called " fire stone " (Feuer stein).] The original word pyrites
has similar reference to the use of the mineral in striking fire.

Quartz (Nos. 1427 to 1433).

Crystals of quartz occur under various conditions in many of the
Neozoic rocks. Some of the finest examples are found in the
Dolomitic Conglomerate, especially in the interior of the potato-
stones of Bristol and the Mendip area. These have already been
noticed (p. 113), but in addition to the specimens exhibited in Case
VII. another is placed here in order to illustrate the minerals
yielded by the Trias (No. 1427).

The agates of the Dolomitic Conglomerate on disintegration
of the rock, may be preserved in the resulting detritus, and
probably in this way the agates of the Litchfield drift have been
derived. These agates are curiously altered, as seen in No. 1428, or
still better in the large series, presented by Spencer G. Perceval, Esq.,
and exhibited in the Table-case of agates on the opposite side of the
museum. In the Litchfield agates there are certain zones which
have become dull and soft so that they adhere to the tongue, whilst
some are reduced to a white opaque substance so soft as to yield
to the finger nail.J Probably some of the layers contain both
crystalline and colloidal silica, and the latter may be dissolved out by
waters containing alkahne carbonates, or organic acids, leaving a
residue which will be porous in consequence of the removal of the
soluble part, and dead white by reflection of light, from the walls
of the solution pores. The effect will be similar to that presented 1 by
the surface of certain weathered flints. Such de-opalised flint is
sometimes known as Passyite.^

Quartz occurs in fairly large crystals under circumstances of
rather exceptional character in the fuller's earth beds worked in the
Lower Greensand at Nuffield in Surrey. The specimen No. 1429
shows the association of the colourless crystallised quartz with honey-
yellow barytes. In some cases the Nutfield quartz presents a tint
distinctly amethystine. It may be noted that the quartz is of
subsequent formation to the barytes and occupies the space
between the barytes-crystals.

*Mem. Geol. Surv. " Geology of Cambridgeshire." By A. J. Jukes-Browne,
•f See, for example, Sir John Pettus's Fleta Minor, 1683.
J " Notice of some Peculiarities observed in the Gravel of Litchfield."
By A. Aikin, Esq. Trans. Geol. Soc, vol. iv. (182 ), p. 426.
§ Lacroix's " Mineralogie de la France," t. iii. (1901), p. 132.

200 MINERALS Of THE NEOZOIC STRAf A.

Some of the best examples of quartz from the Cretaceous beds are
the crystals often found lining the interior of hollow flints from the
Chalk, of which No. 1430 is a specimen. No. 1431 is an example of
chalcedony, or microcrystalline silica, forming a mammillary coating
on the walls of a cavity in a flint, whilst in No. 1432 the chalcedony
hangs from the upper part of the hollow in small pendant stalactites.
The specimen No. 1433 illustrates the curious conoidal fracture of
flint — a character apparently connected with the uniformity of
grain and mechanical isotropism of the flint. No attempt is here
made to represent the varied forms and characteristics of Flint, as a
large series of specimens will be found in the Petrographical collec-
tion, whilst others are seen in Section P of the Horse-shoe Case.

Allophane (Nos. 1434 to 1436).

In 1856 the occurrence of Allophane was noticed at the chalk pits
at Charlton, in Kent, by some of the students of the Royal School of
Mines. Its mode of occurrence was described by Prof. Morris,*
and the mineral was analysed by Mr. A. Dick and by Mr. Northcote,
who was attached at that time to the Royal College of Chemistry.
The allophane, known to the quarrymen as " petrified water,"
occurred as a white, yellow or brown amorphous substance, in nodules
or irregular layers, often lining fissures and funnel-shaped cavities in
the chalk, just at the junction of the Thanet sands (Nos. 1434, 1435).
Mr. Northcote regarded it as a silicate of alumina with a variable
amount of neutral hydrate. f It seems to be a product of the
decomposition of certain aluminous silicates.

Allophane was discovered by the late Dr. Charles Berrill in the
Northampton sand worked for ironstone, and the substance was
analysed by Mr. Douglas Herman. J A specimen is shown in
the Horse-shoe Case.

Related more or less nearly to allophane is the mineral substance
known as Scarbroite — a hydrated silicate of aluminium, with a small
proportion of silica, falling in some cases below 8 per cent. The
mineral was discovered near Scarborough, by the Rev. W. Vernon
Harcourt, and has been described by Mr. Fox Strangways as occurring
in small veins in the Grey Limestone and in the Estuarine series
above. § A specimen of scarbroite is exhibited as No. 1436.

* " On the Occurrence of Allophane at Charlton, Kent." Quart. Journ.
Owl. Soc, vol. xiii. (1856), p. 13. See also Mem. Oeol. Surv. " The Geology
of London." By W. Whitaker, RA., F.R.S., vol. i. (1889), p. 527. Mr.
Whitaker gives a list of the few minerals which occur in the London
district.

f " On the Constitution of Allophane." Phil. Mag. (4), vol. xiii. (1857),
p. 338.

X Quart. Journ. Oeol. Soc, vol. xxvii. (1871), p. 234. See also Mr. Sharp's
paper : " The Oolites of Northamptonshire." Ibid., vol. xxvi. (1870),
p. 307.

§ Mem. Oeol. Surv. " The Jurassic Rocks of Britain," vol. i., Yorkshire,
1892, p. 475.

ALl MINITE, ETC L'<»1

Aluminite or Websterite (Xos. 1437 to 1439).

In the early years of the last century pieces of this substance were
picked up by Mr. Thomas Webster, on the beach between Brighton
and Beachy Head.* It was described as a white substance resem-
bling tobacco-pipe clay, and was at first regarded as pure alumina,
but was shown by Wollaston and Smithson to be a hydrous sub-
sulphate of alumina. f This mineral, called Websterite by most
geologists, but known also as Alumiuite — a name which, according
to the law of priority, it ought to enjoy — occurs typically in the form
of reniform masses, with a micro-crystalline structure, found at the
junction of the Tertiary beds with the Chalk, especially at Xewhaven
(Xos. 1437, 143*). Its origin is not difficult to understand. Free
sulphuric acid is readily formed by the oxidation of pvritic minerals,
and this acid might decompose the silicate of alumina in the clavs of
the Lower London Tertiary series, or in other clays upon the chalk,
with production of an aluminium sulphate.

Many years ago Mr. Spencer G. Perceval called attention to some
deposits of websterite exposed in excavations at several localities
in Brighton, where they occurred a few feet below the surface, in
association with limonite and selenite, as seen in some of these
specimens. J A very large mass of this Brighton websterite will be
found in the Hall of the Museum, under a Table-case on the eastern
side, near the window, and a small specimen is placed in this Case
(Xo. 1439.) The brown ochreous material represents the irou of
the pyrites, whilst the selenite has been formed from the chalk, or
from shells, by the action of sulphuric acid, set free on decomposition
of the pyrites. Some of this websterite is coated with a black-
deposit, in which the late Dr. Flight found manganese and cobalt.

In describing the websterite discovered during the drainage works
in the Montpelier district in the X.W. of Brighton, the late Mr.
James Howell remarked that the mineral was found rather plenti-
fully in chalk districts wherever pyrites was associated with clay.§

Some confusion has been introduced into nomenclature by the fact
that the name websterite has also been given to a certain pyroxenitic
rock. There is consequently the more reason why the name should
be detached from the mineral, and the mineral distinguished as
aluminite.

Calcite {Nos. 1440 to 1444).

Crystals of calcite may occur in the fissures of any calcareous rock,
and are common in many Xeozoic limestones. Such crystals, how-
ever, are generally not equal in size or in beauty of form to those
from the older rocks or from mineral veins.

A few examples of calcite from limestones and other deposits of
Secondary age are here exhibited. In the Triassic beds, calcareous

* Ann. Phil. vol. i. (1813), p. 467.

f Ibid., vol. ii. (1813), p. 238.

; Geol. Mag., vol. viii. (1871), p. 121.

% Eep. Brit. Assoc , Brighton, 1872, pp. 108, 105.

202 MINERALS OF THE NEOZ

*sl\j Q1IVA1&.

spar occasionally occurs, and is usually coloured red with oxide of
iron, as in No. 1440. Crystals lining the potato stones from the
Dolomitic Conglomerate are similarly tinted, as shown in Case vii.
The rock from near Wells, described by Buckland and Conybeare
under the name of "wonder stone," was a breccia containing yellow
transparent crystals of calcite in a dark red dolomitic matrix.*

In the interior of fossil shells calcite is not infrequent. No. 1443
shows the mineral crystallised in the cavity of a Terebratula
from the Great Oolite. No. 1441 represents the columnar
calcite, known from its colour and structure as " sugar candy,"
occurring in fissures in the Portland quarries. Fibrous calcite from
the Purbeck beds is often termed by quarrymen •' beef " — a
name suggestive of its resemblance to the fibres of muscular tissue.
The specimen No. 1442, presented by Clement Reid, Esq., F.R.S.,
is a good example of crystallised calcite from the Upper Chalk of
Corfe Castls.

Calcareous deposits, of stalagmitic and stalactitic character, are
common in the cavities in calcareous rocks of all ages, and are in
course of formation at the present time whenever waters containing
carbonate of calcium percolate through the rocks under conditions
which favour precipitation. Stalactites of recent formation may
often be seen hanging from the soffits of railway arches, for even
when the arch is built of brick the mortar furnishes a supply of
lime. A series of stalactites and stalagmites will be found in the
Collection of rock specimens at the southern end of the Museum.

Jet and Amber (Nos. 1445 and 1446).

A few substances generally regarded as minerals but evidently
formed, directly or indirectly, from organic sources, are here grouped
together, at the end of the series of specimens representing the
mineral resources of Southern Britain. Among these so-called
" organic minerals " Jet occupies a conspicuous place. It appears,
however, from the official statistics that no jet has been obtained in
this country since 1897.

The jet, formerly worked rather extensively at Whitby in York-
shire, occurs there in the Upper Lias shales. It is usually regarded
as a compact variety of lignite, and, indeed, some varieties show th-j
microscopic structure of coniferous wood, but the tissues seem to be
impregnated with bituminous matter, and in many cases the vegetable
structure is completely obliterated. A jet-like substance occasion-
ally forms the mineralising material of certain fossils, especially the
scales of fishes ; drops of liquid bitumen occur in the chambers of
ammonites and in the interior of nodules in the jet rock ; and in-
flammable gases sometimes accumulate in the old workings. It
seems not unlikely that masses of vegetable matter like tree trunks
may have sunk, water-logged, in the black mud of the Liassic sea —
the mud itself partly derived, perhaps, from the disintegration of the

*Mem. Geol. Surv. " Geology of East Somerset." By H-. B. Woodward,
F.R.S., 1876, p. 63.

jjt, amber, etc. 203

Coal Measure shales, and the material thus buried, without access of
air, would undergo conversion into a lignitic substance, whilst a kind
of natural destructive distillation yielded bituminous matter which
saturated the product.* Mr. A. C. Seward finds that much of the
Whitby jet was formed from drifted wood of Araucarian type, f

Jet was formerly obtained from nodules picked up on the beach,
but when this supply became exhausted the cliffs were attacked, and
the jet-rock ultimately worked by simple burrowing.

On the Norfolk coast, in the neighbourhood of Cromer, jet is occa-
sionally thrown up on the beach, especially after east winds. This
appears to be different from Yorkshire jet, and i3 regarded by Mr.
Clement Reid as probably derived from Lower Tertiary beds, buried
under the North Sea . To a similar source must probably be referred
the Amber which is sometimes found on the coast of East Anglia. A
few pieces of such amber are here shown (No. 1446), and some
finer specimens will be found in Section C of the Horse-shoe
Case, including a piece of pale clouded amber, dredged off Yarmouth,
weighing as much as 37 ozs., and another piece, differing markedly
from the former by its deep orange colour, found on the coast of
Cromer, and weighing i'*! ozs.i; The specimens in the tray
No. 1446 were presented by C. Reid, Esq.

Copaline, etc. (Xos. 1447, 1448).

Various mineral resins, more or less allied to amber, yet rarely if
ever suitable for ornamental purposes, occur occasionally in the
stratified rocks of Britain. No. 1447 is an example of such a sub-
stance from the Upper Greensand of Black Gang Chine, in the Isle of
Wight ; whilst No. 1448 is a specimen of the well known fossil resin
from the London ' lav of Higligate, often called Copa/iii£, or High-
gate Resiv. This was first detected nearly a century ago by Mr. B.
G. Snow, a local surgeon, whilst the tunnel was being driven through
Highgate Hill . Sowerby, writing in 1817, speaks of a great quantity
having been found, " perhaps a peck or two,' : § but most of it dis-
appeared by disintegration. Samples were sent by Sowerby to Dr.
Thomas Thomson, who was led from his analysis to regard it as
approaching nearest in character to copal and amber. || Its chemical
properties, however, according to the doctor, threw no light on its

*On the occurrence of jet at Whitby see Mem. Geol. Surv. " The Geology
of the Country between Whitby and Scarborough." By C. Fox-Strangways
and G. Barrow, 1882. " The Geology of North Cleveland." By G. Barrow.
1888 ; and " The Jurassic Rocks," vol. i., Yorkshire. By C. Fox-Stran^. ays.
p. 45? Also. " The Geologr of Yorkshire.': By R. Tate and J. F. Blake.

t Rep Brit. Azsv. for 1903, p. 841

I On East Anglian amber and jet, see Mem. Geo!. Surv. " The Geologv of
the Country around Cromer." By Clement Reid, F.R.S., 1882, p. 133. Also,
" On Norfolk Amber,"- by same author, Trans. Norfolk Nat. Soc, vol. iii.
(1884), p. 601. Hid. vol. iv. (1886), p. 247.

§ " Brjtjsh Mineralogy," vol. v., p. 230.

'I " Description of a Resinous Substance Lately Dug Out of the Earth at
Highgate." Ann. Phil., vol. ii. (1813), p. 9.

7882. r 2

20 i MINERALS OF THE NEOZOIC STRATA.

origin, and could not, to use his words, " facilitate our enquiries into
the revolutions which the southern part of this kingdom has under-
gone, and the various animal and vegetable remains so thickly
scattered in its bowels." As a matter of fact, the substance seems
to be merely a resinous exudation from certain coniferous trees which
flourished on the land drained by the great London Clay River. It
was found not only in small lumps in the clay, but attached to fossil
wood, bored by teredo, and in some cases on septaria, whilst it was
frequently associated with pyrites.

According to Prof. F. W. Johnston, who analysed a large series of
carbonaceous minerals, the Highgate substance is nearly, if not
absolutely, identical in constitution with the gum animS of Cayenne.*
It was this, or a similar body, that was described by Dr. Wetherell,
in 1838, as having been found in the railway cutting at Chalk Farm,
where it was associated with much pyrites, and also in a septarium
at Highgate Archway, close to certain vegetable remains. The
relation of the pyrites to the resin may be sufficiently explained by
the reducing action of the carbonaceous matter.

It seems likely that it was a resin of like character that is referred
to by Dr. John Woodward, when he speaks of " amber, brown and
fossil, found at least thirty feet deep in the pit where they dig clay to
make tiles at Richmond, Surrey " ; and he adds : " The workmen
call it rosin." True amber is said to have been found in the gravel
pits at Kensington.

Certain mineral hydrocarbons have already been referred to as
occurring among the older rocks (p. 178), and other bituminous sub-
stances are occasionally found among the Neozoic strata. These
may assume the solid form of asphalt, or the liquid state of petroleum,
or even the gaseous condition. Natural gas is now obtained indus-
trially at Heathfield, in Sussex, where it appears to rise from sands
and sandstones of the Lower Wealden beds and from certain Purbeck
strata. The occurrence of the gas at Heathfield was described by
Mr. Charles Dawson.f soon after its discovery, and has recently
been the subject of some geological observations by Mr. H. B.
Woodward, t

* " On the Composition of Certain Mineral Substances of Organic Origin :
vi. Highgate Resin, or Fossil Copal." Phil. Mag., vol. xiv. (1839), p. 87.

t " On the Discovery of Natural Gas in East Sussex." Quart. Journ.
Geol. Soc, vol. liv. (1898), p. 564.

J " Notes on the Occurrence of Natural Gas at Heathfield, Sussex." Mem.
Geol. Surv. Summary of Progress for 1902, p. 195.

MINERALS OF SCOTLAND. 'J.U~>

DIVISION 2
MINERALS OF SCOTLAND.
Minerals of the Leadhills District.
[No<. U4!» to I'M.)

A collection fairly representative of the minerals of Scotland is
exhibited, partly in Case XI and partly in Case XII. According to
a List communicated to the British Association in 1901, by Mr. J. G.
Goodehild, there are about l&) species of minerals known to occur in
Scotland.* The collection here exhibited, though containing some
very fine specimens, cannot be regarded as large when compared
with the extensive display of local minerals in the Jioval
Scottish Museum in Edinburgh, which includes the famous
collection made by the late Dr. Heddle. For further information
respecting the minerals of Northern Britain the visitor may be
referred to the comprehensive work on " The Mineralogy of
Scotland," by this authority, published posthumously, under the
editorship of Mr. Goodchild.f

The first group of Scottish minerals exhibited in the Case now
under notice illustrates the well-known ore-deposits of the mining
country around Leadhills, in the south of Lanarkshire, and the neigh-
bouring district of Wanlockhead, on the borders of Dumfriesshire.
Here, in a wild and elevated tract of the Southern Uplands, veins
of lead ore, coursing through rocks of Lower Silurian (Caradoc)
age, have been worked from a very early period.* Documentary
evidence traces the history back to the thirteenth century, but
according to some authorities mining was probably carried on here
during the period of the Roman occupation, or even in prehistoric
times.S

It is not, however, simply the lead-ore which has rendered this
district famous in the annals of British mining. Gold was formerly
found in considerable quantity, and even now grains of the precious
metal may occasionally be obtained by washing the alluvium of the
burns. The gold of Crawford Moor is said to have been discovered
in the reign of James IV., and the celebrated " bonnet pieces " were
minted of this metal. At various periods in the course of the
sixteenth century, considerable activity prevailed, and at one time

* " A List of the Minerals known to occur in Scotland."- Rep. Brit. Ass.,
Glasgow, 1901, p. 649.

f " The Mineralogy of Scotland." By the late M. Forster Heddle, M.D.
Edited by J. G. Goodohild. 2 vols. Edinburgh, 1901.

% The geological structure of the district is described in Mem. Oeol. Surv.
" The Silurian Rocks of Britain, vol. i., Scotland." By B. N. Peach, F.R.S.,
and John Home, F.R.S.E. With Petrological Chapters and notes by
J. J. H. Teall, M.A., F.R.S., 1899.

§ " The Silurian Districts of Leadhills and Wanlockhead, and their Early
and Recent Mining History." By John R. S. Hunter, D.Sc, LL.D. Trans.
Oeol. Soc. Glasgow, vol. vii. (1885), p. 373.

206 MINERALS OF SCOTLAND.

Sir Bevis Bulmer worked to such good purpose that he was able to
present to Queen Elizabeth a porringer made of gold from this
locality. Nuggets weighing several ounces each, in one case reaching
as much as 30 ozs., have been recorded.*

It is probable that the gold of this district has been derived from
the disintegration of pyritic quartz -veins. Heddle refers to a
brown iron-ochre from the Scar Burn, on the upper waters of
Wanlock, which yielded more than five dwts. of gold to the ton.f
This may well have been a gozzany ore, resulting from the alteration
of auriferous pyrites.

At the present time, the Museum is not in possession of any
examples of the gold of Crawford Moor. The few specimens of
Scottish gold exhibited in Wall-case 14 were obtained, in 1869,
from Kildonan Burn, in Sutherlandshire.J

Silver is yielded to a moderate extent by the lead-ore of the
Southern Uplands. In 1902 the mines of Wanlockhead produced
899 tons of lead-ore yielding 4,944 ounces of silver ; whilst those of
Leadhills turned out 730 tons of ore, with 2,555 ozs. of silver.§
Two excellent examples of crystallised galena are here exhibited
as No. 1449.

In the shallow workings of the lodes in the Leadhills district, a
great variety of oxidised products was formerly obtained, including
several species not found elsewhere in Britain, or found only in the
lead-veins of Caldbeck Fells in Cumberland (p. 152). The rarer
minerals were obtained almost exclusively from the Susanna Mine
at Leadhills. Excellent representatives of all these species, such as
are to be found only in collections made many years ago, are ex-
hibited in the Case now under review.

No. 1450, according to an old label, is a specimen of Minium, or
native red lead, from Leadhills. This rare mineral, appearing here
as a pulverulent incrustation, of brilliant scarlet colour, is evidently
an alteration-product of other plumbiferous species. The authenti-
city of specimens of minium in old collections is not always free
from doubt, but there seems no reason to regard this specimen as
other than genuine.

* See " The Discoverie and Historic of the Gold Mynes in Scotland." By-
Stephen Atkinson. Printed by the Banantyne Club, Edinburgh, 1825.
Also, " Early Records relating to mining in Scotland. Collected by R. W.
Cochrane-Patrick of Woodside." Edinburgh, 1878. Reference may be
made to several papers on Scottish gold by Dr. Lauder Lindsay, such as " The
Gold and Gold-Fields of Scotland." Trans. Edin. Oeol. Soc, vol. i. (1870).
p. 105. See too " Historical Notes on the Occurrence of Gold in the South
of Scotland." By Patrick Dudgeon, Min. Mag., vol i. (1877). p. 21. Also:
"The Occurrence of Gold in Great Britain and Ireland." By J. Malcolm
Maclaren. Trans. Inst. Min. Eng., voL xxv. (1904). p. 435.

f " The Mineralogy of Scotland," vol. i., p. 7.

\ On the occurrence and probable source of the Sutherlandshire gold, S2e
Mr. E Greenly's "Notes on the Sutherland Gold-Field." Trans. Edin.
Oeol. Soc, vol. vii. (1899), p. 100. This paper contains a bibliography of the
subject.

§ Home Office Report for 1902, p. 244.

LEAD-ORES OF LEADHILLS. 207

A good suite of specimens, numbered 1451 to 1456, serves to
illustrate the occurrence of Cerussite, or lead carbonate, in the
veinstones of Leadhills. Cavities within the zone of oxidation not
infrequently contained this mineral, crystallised in well-defined
forms, and associated with other oxidised lead-ores in such relation-
ship as to suggest a rather late origin for the cerussite. The crystals
in Xo. 1455 present a blackened appearance, due perhaps to the
action of sulphuretted hydrogen. Mr. Goodchild has suggested
that the lead-grey colour of some of the cerussite may be due to the
presence of lead dioxide. The Leadhills district was at one time
rather remarkable for the beauty and variety of its crystallised
cerussites.*

Pyromorphite, or chloro-phosphate of lead, finds illustration in the
specimens Xos. 1457 to 1460. Whilst some of these examples of
the mineral are of green colour, others are yellow, orange, and even
red. The bright orange-coloured variety, which was raised in the
Susanna Mine, has been sometimes regarded as a chromo-phosphate ;
but Dr. Norman Collie remarks that no chromium is revealed by
the analyses.t

Probably certain compounds of vanadium may be responsible for
the tints in some of the coloured phosphates. Isomorphous with
pyromorphite, is the mineral called Yanadinite, a vanadate of lead,
for which the mines of Wanlockhead have been in their day rather
famous. This rare mineral, as seen in Xos. 1461 to 1404, crystallises
in small hexagonal prisms, but is usually found in globular aggre-
gates, of pale brown colour. Dr. Heddle records a crystal formed
partly of vanadinite and partly of pyromorphite — a striking proof
of the isomorphism of the two species. According to Mr. Goodchild
" the vanadium in the Leadhills Mines may possibly have originated
through the decomposition of the ferro-magnesian silicates present
in the Arenig lavas there, as small traces of vanadium can usually
be detected in the fresh minerals in question." J The wide distribu-
tion of vanadium is attested by the spectroscope.

Some excellent examples of Anglesite, or lead sulphate, are
exhibited here as Xos. 1465 to 1472. These show the characteristic
dagger-shaped crystals, of exceptional size and perfection. The
association of the mineral with decomposed galena in Xo. 1470, at
once betrays its origin. Far more interesting, however, than the
simple sulphate of lead are the crystallised basic sulphates and
sulphato-carbonates, for which the Leadhills district is renowned.

Lanarkite, considered to be the rarest of all the minerals of Lead-
hills, is a basic sulphate of lead, which was originally described as a
sulphato-carbonate. It occurs in small monoclinic prisms, and in
diverging aggregates of long slender crystals ; some of the crystals

* See Mr. J. G. Goodehild's " Contributions to Scottish Mineralogy. "-
Proc. Boy. Soc. Edin., vol. xxiv., part iii. (1902), p. 321.

t " On some Leadhills Minerals.'' Journ. Chan. Soc, vol. lv. (1889),
p. 91.

* •' Contributions to Scottish Mineralogy." Op. cit, p. 338.

208 MINERALS UP" SCO

presenting a pale greenish tint. The characters of the mineral and
the nature of its associates are well seen in the specimens, Nos. 1473
to 1478. According to Heddle this species was found only at the
Susanna Mine. Among the accompanying minerals will be noted
a group of other secondary species, such as caledonite, leadhillite,
Hnarite and cerussite, with galena, the parent-mineral of the whole
family.

The beautiful crystals of Linarite will arrest the attention of the
visitor by their fine azure-blue colour — a colour which has occasion-
ally led to the mineral being mistaken for chessylite, or blue
carbonate of copper. Whilst lanarkite is a basic sulphate of lead
linarite is a basic sulphate of lead and copper. It has already been
referred to in connection with its occurrence at Eoughten Gill
(p. 157), but the Leadhills specimens here exhibited (as Nos. 147!)
and 1480) are even finer than those in Case IX. from the Cumber-
land locality.

Caledonite, one of the rarest minerals of Leadhills, is another basic
sulphate of lead and copper, though originally described as a cupreous
sulphato-carbonate of lead. It occurs in small greenish-blue
crystals of prismatic habit, as shown in the specimens Nos. 1481 and
1482, where it occurs in association with leadhillite and lanarkite.
Dr. Collie suggested that caledonite might be regarded as a hydrated
form of lanarkite, in which lead was partly replaced by copper.

A fine series of specimens, comprised under Nos. 1483 to 1492,
represents the characteristic species named Leadhillite. This is a
basic sulphato-carbonate of lead, occurring in crystals of tabular
habit, belonging to the monoclinic system, and presenting a marked
pearly lustre on the cleavage-planes. According to Dr. Heddle, it
occurred in all the mineral veins of the Leadhills and Wanlockhead
Mines.

Closely related to the true Leadhillite, of which it is probably but a
variety, is the mineral named Susannite, after its occurrence in the
Susanna Mine at Leadhills. Optically it presents uniaxial char-
acters ; but Prof. Groth suggests that this may be due to repeated
lamellar growth.* It has been pointed out by Mr. L. J. Spencer
that three distinct kinds of leadhillite may be recognised : first, the
ordinary monosymmetric leadhillite ; secondly, the susannite
which has been described as rhombohedral ; and thirdly, an ortho-
rhombic type, which he has found in the old lead slags of the
Mendip Hills (p. 108). f Although similar to each other in general
external characters, each kind has probably a definite chemical
composition, and discrepancies in the analyses may be due to
intimate admixture of these varieties. Dr. Collie has called atten-
tion to the apparent inconstancy in the ratio of the sulphate and
carbonate in this species. Nos. 1489 to 1492 are specimens of
susannite, exhibiting its^typical characteristics.

* " Tabellarische Uebersicht der Mineralien." 4 ed. 1898., p. 71.
■f " Leadhillite in ancient lead-slags of the Mendip Hills." Rep. Brit.
Ass., Bristol, 1898, p. 875 ; Oeol. Mag., new ser, Dec. 4, vol. vi. (1899), p. 71.

MINERALS OP LEADHILLS. 209

Ores of zinc occur, to a limited extent, with those of lead in tho
veins of the Leadhills district. Blende, as usual, is associated with
the galena ; but though fine crystals are occasionally found they
are not common, and there are at present no examples in the
collection. The silicate of zinc, previously noticed under the name
of Hemimorphite, occurs at Wanlockhead ,sometimes in acicular
crystals, but more often in massive or botryoidal forms, not in-
frequently invested with variously coloured pyromorphite. As
an example of its comparatively recent formation, Dr. Heddle
records its occurrence as a chalky deposit on some old timber at
tlic Bay .Mine, Wanlockhead.* Calamine, or carbonate of zinc,
is not included as a Scottish mineral in Mr. Goodchild's List. In
the year 1902 there were raised at Wanlockhead 110 tons of zinc-ore.

Associated with the lead and zinc ores of the Leadhills tract,
copper-pyrites and its various alteration products occur in sub-
ordinate quantity. No. 1493 is a specimen of Malachite, showing
by its association with galena and with cerussite that both the lead
and the copper ore have suffered conversion into carbonates. In
the rare species Aurichalcite, represented by Nos. 1494 and 1495,
copper and zinc occur together as a basic carbonate, though free
carbonate of zinc, as previously noted, is not recorded from these
deposits. The aurichalcite occurs in delicate acicular crystals,
forming divergent groups, of a pale green or sky-blue colour,
associated with the rare species, lanarkite. With these Scottish
specimens of aurichalcite may be compared the examples of the
same mineral from Cumberland in Case IX. (p. 158).

Several specimens are exhibited in illustration of the various
sparry minerals which occur in the veinstones of the Leadhills
Mines. No. 1496 is a geode of barytes, and No. 1497 a specimen of
eaJcite in opaque white scalenohedra, on which are seated small
saddle-shaped crystals of pale brown dolomite. Most of the Lead-
hills calcite contains, according to Dr. Collie, more or less carbonate
of lead, and when the proportion becomes notable the mineral
is usually called Plumbocalcite — a name given to it in 1829 by Prcf.
J. W. Johnston. This plumbiferous calcite occurs in dull white
rhombohedra, rather denser than pure calcite. It is regarded as
an isomorphous mixture of the carbonates of lead and calcium
in variable proportion, and is theoretically interesting since it
suggests the existence of a rhombohedral carbonate of lead. This
compound is therefore probably dimorphous, forming an ortho-
rhombic species — the ordinary cerussite, which corresponds to
aragonite, and a rhombohedral species not yet known in a free
state. Just as the two rhombohedral species occur together in
plumbocalcite, so the two orthorhombic species are associated
in the mineral called Tarnowitzite.'f Dr. Norman Collie has published
analyses of Phimbo-aragonite from Leadhills, proving that the

*"The Mineralogy of Scotland, vol. ii., p. 73.
f See Prof. Miers' " Mineralogy," p. 227.

210 MINERALS OP SCOTLAND.

aragonite of this locality may contain a small proportion of lead
Carbonate, though his specimen was not so highly plumbiferous
as the typical tarnowitzite of Silesia.*

Some excellent examples of Aragonite from Leadhills are exhibited
here as Nos. 1501 to 1503. In one specimen (1501) the mineral
occurs in white slender crystals on calcite, whilst in the other
specimens the crystals are of a delicate sea-green tint, acicular
in habit and disposed in divergent groups. Dr. Heddle examined
some green crystals from Leadhills, which had been regarded as
strontianite, but found that they contained only 1-7 per cent,
of carbonate of strontia, and were practically aragonite. f

With regard to the origin of the minerals at Leadhills, it is probable,
as Mr. Goodchild suggests, that although the metalliferous veins
may have had a very complicated history, the introduction of
much of the mineral matter may have been due to the uprise of
thermal solutions in fault-fissures during the later phases of volcanic
activity in Tertiary times.

Minerals prom Strontian.
(Nos. 1505 to 1516.)

Although the minerals of Strontian ought strictly to be placed
with those of the Highlands in Case XII., it has been deemed de-
sirable to sacrifice the topographical arrangement in order to utilise
the space left in Case XL at the end of the Leadhills series. Hence
the minerals of Strontian are here placed in immediate sequence to
those of Leadhills.

Deposits of lead-ore near the little village of Strontian, in Argyll-
shire, were opened up at the beginning of the eighteenth century,
and continued to be worked for rather more than 150 years. The
ore occurred in veins, coursing through gneissose rocks, near their
junction with the granite. Nos. 1505 and 1506 are samples of the
galena, and many other specimens will be found in Wall-case 45.
The museum is fortunate in possessing a rather large series of the
Strontian minerals, principally from Bellsgrove and Fee Donald
Mines, presented by the late Sir James Miles Riddell, Bart., at the
close of the Great Exhibition of 1851, where they had been exhibited.

In Section I. of the Horse-shoe Case are several examples of the
Calcite from the Strontian lead-lodes, whilst in the case now under
notice the species is represented by Nos. 1507 and 1508. One of
these specimens shows the calcite in the form of " Slate spar," or
Schieferspath — the tabular habit being determined by development
of the basal pinacoid. The opaque white plates of this spar are
seated on brown calcite, which is crystallized in obtuse rhombohedra,
deeply striated and marked by dark radiating lines running along
the short diagonals of the rhombs. Barytes also occurs in the
vein-stone of the Strontian lead-lodes.

* J (mm. Chetn. Soc, vol. Iv. (1889), p. 95.

•(■ '• Minerals New to Britain.". Min. Mag., vol. v. (1884), p. 22.

MINERAL-; OF STRONTIAN - . 211

The vlaage of Strontian is famous for having given its name to
the element strontium. This metal occurs here in the form of the
carbonate, known &*■ Strontianite. It appears that the mineral was
found as far back as 17G4, and was at first regarded as carbonate of
baryta. But in consequence of its property of imparting a reddish
colour to flame it was suspected by Crawford, in 1790, to contain a
new earth — a suspicion independently expressed by Cruikshank,
and soon afterwards confirmed by Dr. Hope, of Edinburgh, who in
1792 determined the existence of a peculiar substance which he
named after the Strontian spar in which it was discovered. The
metal strontium was isolated by Daw in 1808.

Strontianite is here represented by Nos. 1509 and 1510, whilst the
visitor is referred for other and larger specimens to Section G of the
Horse-shoe Case. Distinct crystals are rare, but the mineral usually
occurs in fibrous masses, the colour of which is sometimes pale green
as in No. 1509, sometimes dark brown as in No. 1510. Strontianite
is an orthorhombic species, isomorphous with witherite and aragon-
ite. The mineral frequently contains barium, partially replacing the
allied strontium.* Just as witherite may be converted into barytes
by the action of certain sulphates, such as those resulting from de-
composing pyrites, so strontianite may be altered to celestite ; and
it is not surprising, therefore, to find that this species occasionally,
though rarely, occurred at Strontian.

The remaining specimens in this Case represent two rather rare
and interesting species, known as brewsterite and harmotome —
minerals belonging to the group of hydrous silicates termed zeolites,
to which attention will be specially directed in the description of
Case XII. (p. 215). Nos. 1511 and 1512 show the Brewsterite in small
brilliant crystals of prismatic habit, belonging apparently to the
monoclinic system. The crystals are striated longitudinally, by
repeated twinning, and present a pale yellowish brown colour.
In No. 1512 the crystals are seated on strontianite. The mineral is
a hydrous silicate of aluminium, strontium, barium and calcium,
and may be regarded as a kind of heulandite (p. 217) in which
calcium is partly replaced by strontium and barium. It was found
chiefly in the Bellsgrove lead-mine, and was described by Mr. Brooke,
who named it after Sir David Brewster (b. 1781, d. 1868).

Although the zeolites are characteristic minerals in the cavities
of eruptive rocks, they also occur to a limited extent in certain
mineral veins. This is notably the case with Harmotome, which
occurs typically in the silver-lead veins of Andreasberg, in the
Hartz, as also in the lead-lodes of Strontian, especially in the old
BellscTove Pit. It is a zeolite which, like brewsterite, contains
barium, but, unlike brewsterite, no strontium. The mineral
crystallizes, it is generally believed, in the monoclinic system, but
always in twins ; and a characteristic habit is that of two complex
sub-individuals interpenetrating, so as to produce a cruciform

* " Analysis of a sample of Strontianite, from Strontian, Argyllshire.".
By W. Ivison Macadam. Min. Mag., vol. vi. (1886), p. 173.

212 MINERALS OF SCOTLAND.

group, whence the name "cross stone," which is sometimes
applied to this species. The crystals from Strontian are bold and
sharply defined, often of opaque white colour. The small colour-
less crystals of harmotome are sometimes distinguished as a variety
under the name of Morvenite, a name derived from a locality in
Argyllshire. The characters of the species are well represented by
the specimens Nos. 1513 to 1516. Some of these show the harmo-
tome associated with calcite, and it occurs also in companionship,
as might perhaps be expected, with the other barium-bearing
minerals, barytes and brewsterite.

The zeolites in the veins at Strontian may have been derived from
the alteration of the felspars in the neighbouring granitic rocks ;
but although certain felspars contain barium the source of this
element is more likely to be explained by reference to the barytes
which occurs in the lodes. As Mr. Goodchild remarks, harmotome
is one of the latest formed minerals in the veins at Strontian. It is
suggested by this authority that the rocks of Strontian may have
been covered by Tertiary basalts, and that the metalliferous mine-
rals may have been introduced into fissures by the uprise of
thermal waters towards the close of the volcanic period. The zeolites
are probably of subsequent formation.*

* " The Natural History of Scottish Zeolites and their Allies." Trans.
Oeol. Soc. Glasgow. Supplement, ^ol. xii., 1903.

MINERALS OF THE MIDLAND VALLEY. li!3

CASK XII.

DIVISION 1.
MINERALS OF SCOTLAND.
Minerals of the Midland Valley.
(Xos. 1517 to 1560.)

Many of the eruptive rocks which are so extensively developed in
the great Midland Valley of Scotland yield various minerals of
secondary origin, especially zeolites, of which a representative
collection is here exhibited. Such minerals occur usually in the
vapour cavities of the vesicular lavas, chiefly of andesitic type,
which are referable to the early part of the Carboniferous period.
Most of the specimens are from the volcanic rocks of the Clyde
plateau — some from the south side of the estuary, notably from
Boylestone Quarry in Renfrewshire, and others from the Campsie
and Kilpatrick Hills, on the north.*

In addition to the zeolites, a few other minerals occur in these
ancient lavas. No. 1517 is a specimenof the Xative Copper occasion-
ally found in Boylestone Quarry, near Barrhead. This example,
presented by Mr. Graham of Craigallian, shows the metal as a
brilliant film on a joint-plane of the rock, as though electro-deposited
on the wall of a fissure. Mr. Goodchild has suggested that in such
cases the metal may have been dissolved out of the eruptive rock
through which it was disseminated, and reduced perhaps from the
state of carbonate by decomposing organic matter. f He also points
out that in this quarry the native copper occurs occasionally as
enclosures in calcite, and that the crystals of calcite are then more
than usually complex in form. The metal is likewise found here in
association with prehnite, to which it sometimes imparts a brown
colour.

The association with prehnite and calcite rather recalls the con-
ditions under which native copper occurs in the amygdaloidal
diabase of the great copper-mining region of Lake Superior, where
the metal is associated with these and other secondary minerals,
including various zeolites. It is supposed that here the copper has

* For a description of the rooks of this district see Sir Archibald Geikie's
work : " The Ancient Volcanoes of Great Britain." London : 1897, vol. iv.,
p. 379. Caps. zxiv. and xxv. are devoted to a detailed description of ihe
Carboniferous volcanic plateaux of Scotland. For a full description of the
zeolites consult Mr. Goodchild' s paper cited above.

+ " The Scottish ores of Copper in their Geological Relations." Rep.
Brit. Assoc, Glasgow, 1901, p. 647.

214 MINERALS OF SCOTLAND.

been reduced from cupriferous solutions by the action of substances
containing iron in the ferrous state, such as the augite and the
magnetite of the eruptive matrix.* Senarmont showed long ago
that copper-bearing solutions were readily reduced by being
moderately heated with various oxidisable bodies.

Possibly the formation of native copper in the narrow crevices of
rocks may receive illustration from Prof. Becquerel's experiments on
electro-capillary action. He obtained deposits of metallic copper
by allowing a cupric solution, like the nitrate, and a solution of
sodium sulphide to react on each other by very slow diffusion in
capillary spaces.f

As metallic sulphides are rather uncommon in amygdaloidal
rocks, the occurrence of the rare sulphide of cadmium, with prehnite,
in the Carboniferous lavas of Eenfrewshire, is peculiarly interesting.
This compound, forming the species called Greenockite, is represented
by Nos. 1518 to 1520 — five specimens from the original locality
near Bishopton. It was in piercing the hard rock to form the long
tunnel at this part of the Glasgow and Greenock Railway that the
mineral was originally brought to light. It was described as a new
species by Prof. Jameson, who named it after Lord Greenock, after-
wards Earl Cathcart (b. 1785, d. 1859) by whom it had been de-
tected.J The crystals were measured by Mr. Brooke, and analysed
by Prof. Connell.§

Greenockite, as seen in the specimens here exhibited, occurs in
small sharply-defined hemimorphic crystals, referable to the
hexagonal system, and presenting a yellow colour, inclining to
orange, with a brilliant, rather adamantine lustre. The mineral
was originally mistaken for zinc-blende. Sulphide of cadmium does
indeed occur in certain kinds of blende known from the Bohemian
locality as Przibramite ; and the two sulphides — those of zinc and
cadmium — belong to an isodimorphous group. Hexagonal sulphide
of zinc, in crystals much like those of Greenockite, constitutes the
species distinguished by Priedel as Wilrtzite. It is notable, too, that
Sidot obtained zinc sulphide in hexagonal crystals by strongly heat-
ing either the artificial amorphous sulphide or common blende.jl
Sidot's hexagonal blende is used for fluorescent screens in
experiments on radio-activity.

The specimens numbered 1521 to 1524 are excellent examples of
the geodes formerly found in the andesitic lava so largely quarried
as " whinstone " at the back of Gourock, near Greenock, in

* '^Tke Deposition of Copper by Solutions of Ferrous Salts." By.H. C.
Biddle. Journ. OeoL, vol. ix. (1901), p. 430.

f " Note sur les reductions metalliques dans les espaces capillaires."-
Comptes Hendus, vol. lxxxii. (1876), p. 354.

% " Notice of Greenockite, a new Mineral Species-of the order Blende.''
Ed. New. Phil. Journ., vol. xxvm. (1840), p. 390.

§ " Chemical Examination of Greenockite, or sulphuret of Cadmium-"- By
Arthur Cbnnell. Ibid., p. 392.
i|.".Recherches sur la cristallisation de quelques sulfures metalliques.''
Comptes Eeiidus,t. lxii. (1866), p. 999,

idJUTES.

21'

Renfrewshire. These drusy cavities were lined with crystals of
calcite. quartz and fivorite. It will be noted that some of the calcite
is tinted pink. An analysis of the pink calcite of Gourock yielded
Dr. Heddle i • 27 per cent, of manganous carbonate.* The fluor-spar
occurs in dark purple cubes, seated on the calcite, and it has been
remarked that of all minerals in these druses the fluor is the latest
formed. f It is notable that fluor-spar, so common in many parts
of England, is decidedly rare in Scotland.

A rather extensive series of specimens, mostly from the Kilpatrick
Hills (Xos. 1.J2.J to lo52) illustrates the group of Zeolites, which are
developed in exceptional beauty and variety in some of the Carboni-
ferous lavas of the Clyde basin. The zeolites constitute a well-
marked group of crystallised hydrated silicates, all containing
aluminium, and most ot them likewise containing either cal-
cium or sodium, or in some cases both. Usually the zeolites appear
to be secondary products, resulting mostly, if not exclusively, from
the alteration of various felspathic and felspathoid minerals,
especially the lime-soda felspars. Some have indeed been regarded
as hydrated plagioclase. Connected with the presence of water is
the fact that these zeolites are softer and less dense than the felspars.
their specific gravity being about 2-2. The zeolites are rather
unstable minerals, and it is sometimes noticed that one species
passes into another.

It was observed by 'Jronstedt, in the early davs of mineralogy,
that most of these minerals intumesce when heated before the blow-
pipe, whence they came to be called zeolites, or " boiling stones.''
They are readily decomposed by acids, and, as first noticed by
Bergmann, many of them when so treated gelatinise.

The condition in which the water occurs in the zeolites has been
the subject of much discussion. In some cases it may occur parti}'
as water of crystallisation and partly as hydroxy] belonging to the
silicate molecule. The water of crystallisation appears to be very
loosely held, being readily lo.-t and regained, according to the dry-
ness or the humidity of the surrounding medium. With the loss of
water, the optical properties of the mineral are affected. The de-
hydrated zeolites may in certain cases be caused to absorb other
substances than water, even various colouring agents, as shown by
the experiments of Friedel.

It is notable that certain zeolites occur in the red clays of the
deep-sea floor, as described by Sir John Murray and the late Prof.
Itenard. Notwithstanding the low temperatuie prevailing in
abyssal waters, certain chemical reactions go on, which result in the
decomposition of the basic volcanic rocks by means of sea-water,
and the formation of zeolitic minerals, like phillipsite. The origin
of such minerals is therefore similar to that of the zeolites in
amygdaloidal rocks, although the conditions of occurrence seem £.0

* Trans. Roy. Soc, Edin., vol. xxvii. (1^7 o), p. 499.

f " Miscellaneous Xotes on Chemical Geology." By Wallace Young.
Trans. Geol. Soc. Glasgow, vol. iiL (1871), p. 3J,> .

216 MINERALS OF SCOTLAND.

different. Moreover Prof. Lacroix has shown that in the Pyrenees
zeolitic minerals are in course of formation at the present day by
the decomposition of rocks under the influence of water from
melting snow.* Such an origin however, seems to be rather
exceptional for the zeolites, and in most cases such minerals were
probably formed at ratber an elevated temperature.

By prolonged action of thermal waters on the concrete at certain
Roman stations in France, several species of zeolites have been pro-
duced. Zeolites also occur in mineral-veins, especially in those which
carry lead, with calcite in the gangue ; and their occurrence in the lead
lodes of Strontian under these conditions has already been noticed
(p. 211).

It was shown by Wohler, in 1848, that powdered apophyllite is
soluble in water, when heated in a closed tube to 180° C. ; and
C. Doelter has since found that most zeolites dissolve in pure water,
at temperatures between 120° and 160°, whilst the solubility is still
more marked when carbonic acid is present. On cooling, the zeolite
separates from the solution in crystals. Sir A. Geikie believes that
in many cases the amygdales, or mineral-kernels in lavas which
were once vesicular, may have been deposited before the rock had
completely cooled.f — a view also held by Mr. Harker with regard
to the zeolites of Skye (p. 221).

The mineral called Prehnite, of which a rather fine suite of speci-
mens is here exhibited (Nos. 1525 to 1531), can hardly perhaps
claim a place among the true zeolites, inasmuch as all the water
seems to be basic, so that it is not strictly a hydrated silicate ; and
further it is only slightly attacked by acids, whilst its hardness and
density are greater than in typical zeolites. Nevertheless, it often
occurs in association with the zeolites and was formed apparently
under similar conditions, being found in amygdaloidal rocks, as
well as in veins. It frequently forms botryoidal and mammillated
masses, crystalline in structure, and usually of green colour, though
sometimes brown. % The association of prehnite with copper is
rather characteristic, and the brownish tint is sometimes referable
to minutely disseminated particles of the native metal, whilst the
green colour has been referred in some cases to the presence of
chrysocolla, in others to chlorite or perhaps to epidote. Prehnite
was a very common mineral at Boylestone Quarry in Renfrewshire,
and at Bowling Quarry in Dumbartonshire.

Associated with the prehnite, as shown by some of these speci-
mens, there commonly occurs the zeolite called Thomsonite (Nos.
1532, 1533). This is a lime-soda silicate, generally in white or

* " Sur la formation de zeolites sous 1' influence du ruissellement superfioiel' '
Comptes Rendus, t. oxxiii. (1896), p. 761.

f " The Ancient Volcanoes of Great Britain.' - Vol. ii., p. 189. The
reference is here to the amygdaloidal rocks of Tertiary age.

% The character of these curved aggregates of prehnite crystals has been
studied by Mr. Goodchild, in his paper on " The Natural History of the
Scottish Zeolites' - already quoted.

ZEOLITES .'I i

colourless cry otah, of acieular or columnar habit, arranged in radia-
ting groups. Aiming the other minerals exhibited here may be meii-
tioned tlie delicate fibrous zeolite known as wcsolitc (Xo. 1534).
The commonest of the fibrous zeolites is termed natrolite ; and
probably the mineral known as gut act iff (Xos. 1535, 153fi) is an
isomorphous mixture of natrolite and seolecite. whilst the zeolite
named croealite (No. 15:'. 7) may also be regarded as a variety of
natrolite.

Of all the zeolites in this case the most attractive to the eve are
the brick-red crystals of Stilbite (Xos. 153s to 1541) and of HeiJcwditP
(Xos. 1542, 1544).* These two minerals have much in common.
Both are lime-zeolites, apparently crystallising in the monoclinic
system. The stilbite not infrequently occurs in sheaf-like aggre-
gates of crystals, whilst the heulandite has quite a characteristic
habit, the crystals being perhaps best described as coffin-shaped.
The pearly lustre on the cleavage planes of the heulandite is worthv
of notice. The red colour has been referred to the presence of
included scaly crystals of gothite. or oxide of iron ; but Dr. Haugh-
ton regarded the colour of some red heulandite which he examined
as due to the molecular condition of the mineral. f Very notable
is the specimen, No. 1540, showing the red stilbite embedded in a
large cleavage rhombohedron of calcite, where the stilbite is
obviously the mineral of earlier formation. " There may be some
connection," says Mr. Goodchild, " between the colour of the stilbite
and the lithological nature of the rock from which it has been
derived." The brick-red minerals occur in the andesitic lavas of
Stirlingshire and Dumbartonshire, and are labelled in most collec-
tions as coming from the C'ampsie Hills. J The red heulandite has
been also recorded from Little Cumbrae.§

But little need be said about the other zeolites shown here.
Analcite, or Anatcime (No. 154*), is exceptional among zeolites in its
crvstallisation, inasmuch as it occurs in icositetrahedra, resembling
those of leucite — a mineral to which it seems to be related. The
crystals of analcite are remarkable for their optical behaviour. The
mineral called Cluthalite (Xo. 1545) is perhaps an altered analcite.
Chabazite (Xo. 1546) occurs well crystallised in rhombodehra, which
have a cube-like appearance, rather suggestive of crystals of fiuor.
Twin crystals are not infrequent. The most unstable of all the
zeolites is the efflorescent mineral which received the name of
iMumontite (Xo. 1547) after an old French mineralogist, Gillet de

* The mineral here called stilbite is termed by many Continental mineral-
ogists Desmine, whilst our heulandite is often known as Stilbite. dome of
the zeolites described above as "apparently monoclinic" may really be
anorthic.

+ Journ. Geol. Soc, DvMin, vol. viii. (1860), p. 234.

+ See " On New Localities for Zeolites." By Prof. M. Forster Heddle.
Trans. Owl. Soc. Glasgow, vol. ix. (1893), p. 72. The author failed to find
them in the Campsie Hills.

8 " A visit to the Island of Little Cumbrae, with some notes on its Miner-
als " By James Xeilson. IbvL, p. 373.

' 7882. '•'

21 8 MTNEKALR OF SCOTLAND.

Laumont. Edingtonite (No. 1549) is rather notable inasmuch as it
contains barium, and to this extent bears some relation to the
zuoliteii already described as harmutome and brewsterite (p. 211).

Several specimens pf Pectolite are here exhibited (Nos. 1550 to
1552). This mineral can hardly be regarded as a true zeolite, yet
it occurs under very similar conditions, being often found as a
secondary mineral in the vapour-vesicles or in the fissures of old
basic lavas. It generally forms tough, radiated masses, composed
of fibres which are often silky in lustre. In certain cases it is
pseudomorphous after analcite. Some of the specimens, of rather
greenish-grey colour, are from the Ratho quarries, near Edinburgh,
and have hence been described under the name of Ratholite. They
occur in an intrusive sheet of dolerite, in the Lower Carboniferous
strata.

Following the zeolitic group of minerals comes a small series
illustrating the characters of Scottish agates. (Nos. 1553 to 1560).
Like zeolites, the agates occur usually in the steam cavities of
eruptive rocks, as secondary minerals resulting from the decomposi-
tion of the matrix ; like zeolites, again, they occur occasionally in
veins. In Scotland the best agates are derived from the andesitic
lavas of the Lower Old Red Sandstone ; and Mr. Goodehild has re-
marked that since they occur in the conglomerate of the Upper Old
Red Sandstone, some at least must have been formed within the
limits of time represented by these rocks. On the disintegration of
the matrix the agates may weather out, and be found loose in the
soil as " Scotch pebbles." The polished sections of pebbles, Nos.
1553 to 1557, are from near Montrose.

An agate consists of alternating layers of various siliceoas minerals,
especially chalcedony, but including also cachalong, quartz and
opal . These minerals have been deposited from siliceoas solutions,
which gained access to cavities in the old lava. It generally happens
that the walls of the cavities are immediately lined by a deposit of
the green earthy minerals known as celadonite and delessite — minerals
which have resulted from the decomposition of augite, or some
other ferro-magnesian mineral in the eruptive rock. Upon this
" priming," to borrow Mr. Goodchild's expressive term, the chalce-
dony may be deposited either directly or with an intervening layer,
which, according to Dr. Heddle, may be zeolitic. Gelatinous
silica was deposited in the interior of the cavities, in most cases
equally around the whole internal space, the material having secured
adhesion to roof and wall as well as to the floor. Successive de-
posits, more or less variable in character, were thrown down in regu-
1 ar sequence, layer upon layer, so that a transverse section of an agate
displays a zonal pattern due to the cut edges of the deposits.

Many agates exhibit tubular orifices or cracks which appear to
have served as channels for the passage of the siliceous solutions.
They were formerly regarded as inlets of infiltration, but G. Lange
many years ago suggested that they might be channels of egress,
through which the solution, after deposition of more or less of its
siliceous burden, bad been expelled. Dr. Heddle, who made a.

MINERALS OF THE IIK.'IIL \\DS. 219

special study of agate;,, al.,u rt-uarded these channels as " tube;; of
escape," bclirxinji that the solution from which tlie silica had been
precipitated passed out on the introduction of a stronger solution,
by osmotic action.*

In some cases, as seen in Xo. 1556, the siliceous minerals may
form horizontal deposits on the floor of the cavity, producing an onyx;
in other cases the deposits may hang from the roof of the cavity
as stalactitic chalcedony ; or they may be deposited over and
around rugosities of the walls and floors, forming concentric deposits,
circular on section, known as rye ip/air. In the tray Xo. 1558 are
two eye-agates from the Path of (Jondie in Perthshire ; X"o. 155!)
is a specimen of moss-agate from Dunbar, and No. 1560 a polished
slab of red jasper from Campsie Glen. A large collection of polished
specimens of Scottish agates and jaspers will be found in Sections
P. and <I> of the Horse-shoe Case ; and hence it has not been deemed
necessary to exhibit a large number here. The Ludlam collection
was far from rich in examples of such minerals.

Minerals of the Highlands.

(Nos. 1561 to 1572.)

For convenience of space the minerals from the lead-mines of
Strontian, in Argyllshire, have been placed in Case XL, in juxta-
position with the ores of the LeadhiUs district. Comparatively
few other minerals from the Highlands of Scotland are exhibited
in this collection. The specimens numbered 1561 and 1562 are
good examples of the red variety of epidote, named by Sir David
Brewster, Withamite. f This mineral occurs in the altered lavas
of the Lower Old Red Sandstone of Glencoe, in Argyllshire,
where it was first detected in 1R24 by Henry Witham. Brewster
observed its remarkable dichroism ; and in recent years its optical
characters have been fully studied by Prof. Lacroix, who has
pointed out their relation to those of epidote and piedmontite — the
latter a manganese-epidote.J Dr. Heddle found in the Withamite
of Glencoe - 138 per cent, of manganous oxide.§ According to Mr.
Goodcbild the mineral has resulted from the alteration of celadonite,
itself probably due to the decomposition of the pyroxene of the
eruptive rock in which it occurs. Withamite has recently been
found by Mr. Muff, of the Geological Survey, in a dyke at the
Meeting of the Three Waters. ||

* On Scottish agates see Dr. Heddle's paper " On the Structure of Agates."
Trans. 6W. Soc, Glasgow, vol. xi., part ii. (1900), p. 153 ; also- his " Miner-
alogy of Scotland," vol. i. p. 58 ; and Mr. Goodchild's paper " On the Genesis
of some Scottish Minerals."- Proc. Phys. Soc, Edin., vol. xiv. (1899), p. 191.

| " Description of Withamite, a new mineral species found in Glencoe. '-
Edin. Journ. 8c, vol. ii. (1825), p. 218.

% " Proprietes optiques de la Withamite." Bull. Soc. Min. Fr , voJ.'x.
(1886), p. 75.

§ " Minerals new to Britain." Min. Mag., vol. v. (1884), p. 15.

|| " Summary of Progress" for 1903, p. 55.
78S2. 9 2

220 MINERALS OF SCOTLAND.

The great granite masses of the Central Highlands have yielded
a few notable minerals, such as the well-known Co. irngorm. This
is a variety of quartz, of smoky or yellow tint, named after the
mountain in Banffshire, where it occurs in drusy cavities in veins
of granite running through the main mass. In order to obtain the
cairngorm, pits were formerly dug in the disintegrated part of the
granite, and the mineral was found as loose crystals in the kaolinised
material. Rolled crystals occurred in the bed of the River Avon.

As Mr. Cunningham Craig remarks, the veins represent intrusions
of the acid magma into fissures of contraction in the granite, and
the quartz has probably crystallized from highly siliceous solutions
which filled the cavities in the veins.*

In addition to the specimens shown here (Nos. 1565 to 1568),
a fine series of cairngorms, including many cut specimens of great
beauty, will be found in Section N. of the Horse-shoe Case. It
should be noted that brown and yellow quartz is sometimes im-
properly called "topaz," or "smoky topaz," a practice not
uncommon in trade and even in scientific writings.

The fine specimen of smoky quartz, No. 1568, presented by
G. Barrow, Esq., is from Banchory in Aberdeenshire.

Associated with the smoky quartz of the Cairngorm district, and
occasionally occurring in the bed of the Avon, were formerly found
crystals of true Topaz. Some of the largest have been obtained from
Benabourd (Beinn a' Bhuird), in the Aberdeenshire part of the
granite mountains, whence several specimens, each more than a
pound in weight, have been recorded. The collection includes
some excellent examples of Scottish topaz (Nos. 1569 to 1572),
illustrating the crystalline forms, the characteristic basal cleavage
and the typical tints of the mineral. Most of the specimens are of
pale blue colour, inclining in certain parts to a reddish brown tint,
whilst some are practically colourless. Beryl occasionally accom-
panies the topaz of the granite of the Grampians, as is the case
in so many other localities. Reference has already been made
(p. 25) to the probable origin of topaz in granitic rocks by
pneumatolytic action.

Two specimens of RutUe, the most common of the three species
of titanium dioxide, are here exhibited. This mineral not in-
frequently occurs in quartz veins in the crystalline schists. No. 1 563
from Killin, in Perthshire, shows the rutile in reddish-brown acicular
crystals penetrating quartz ; whilst in No. 1564 it occurs as a
stout prismatic crystal, longitudinally striated, associated with
muscovite and quartz. It is notable that in the latter specimen
the crystal has been bent and broken, and the fragments cemented
together by quartz. Prisms of tourmaline sometimes exhibit
similar fracture and cementation.

Brief reference may here be made to the recent discovery,
by the Geological Survey, of Cassiterite in the granite gneiss

* " On Cairngorms.'- By E. H. Cunningham Craig, B.A. Rep. Brit
4ss-, Glasgow, 1901, p. 654.

ZEOLITES. 221

of Cam Chuinneag in Ross-shire.* Tin.- di,>eo\ery is of special
interest, inasmuch as tin-stone, though found in England and
Ireland, had not previously been known to occur in Scotland. It
is notable that the cassiterite is here found under exceptional
conditions, being associated with much magnetite but without
tourmaline, and with but little quartz. The mode of occurrence
is at present (1904) fully illustrated in a table case, placed near the
collection of Scottish Minerals.

Minerals of the Western Isles, Etc.
{Xos, 1573 to 1584.)

Many of the basic lavas of Tertiary age, which occur in the
Western Isles of Scotland, spreading out as extensive plateaux or
rising into tabular hills, enclose in their vesicular cavities a number
of zeolitic minerals similar to those already described as occurring
in the older volcanic rocks of the Midland Valley. Such minerals
are represented here by a small suite of characteristic specimens
from the Isle of Skye, principally from the rocks of Storr, in the
northern part of the island.

According to Mr. Harker, who has made an elaborate study of
the Tertiary igneous rocks of Skye, the minerals of the amygdaloidal
basalts were formed from the alteration of the rocks not by ordinary
weathering but by the action of heated water, probably of volcanic
origin, soon after the extrusion of the lava : indeed, their formation
may represent the final phase of volcanic activity.t It is interesting
to note that, by thermal metamorphism, the zeolites have in some
cases been transformed to felspar — apparently a reversion to their
original condition, due chiefly to loss of water.

Among the zeolites of Skye here exhibited are specimens of Stilbite
(Xos, 1573 to 1576), showing the mineral in white crystals, with
pearly lustre on the cleavage faces, the crystals being, in some cases,
aggregated in sheaf-like groups, and in others displayed in radiating
forms. Laumontile is illustrated by No. 1577, where the white
efflorescent mineral is partly coating crystals of stilbite. Xo. 1578
is a specimen of Chabazite, in which the mineral is seen in white
rhombohedral crystals, rather recalling the general aspect of fluor-
spar. Analcite, or Attalcime, is represented by Xo. 1579, which
shows the sharply defined white icositetrahedral crystals so charac-
teristic of this species. According to Dr. Heddle the form in the
Tertiary traps of the Hebrides is invariably the simple icositetra-
hedron, whilst in the paheozoic lavas of Scotland the species some-
times shows faces of the cube. J

* " Summary of Progress " for 1903, p. ."•*.

\ Mem- Oeol. Su.ro., "The Tertiary Igneous Rock- of Sky.'' By Alfred
Harker, M.A., F.R.S., with Notes by C. T. Clough. M.A., 190-1.

+ " On Analcime with New Forms." Trans. Edin. Geol. Soc., vol. vii.
(1899), p. 241. Also " Mineralogy of Scotland," vol ii., p. 103.

222 MINERALS OF SCOTLAND AND IRELAND.

No. 1580 is a specimen of Mesolite, in which white needle-like
crystals spring from the walls of a drusy cavity in basalt, 'whilst No.
1581 is an example of the lime zeolite known as Gyrolite. With
the zeolites, though perhaps in strictness hardly belonging to the
group, is placed an example of Pectolite (No. 1582), a mineral of
which a brief notice has already been given (p. 218).

The specimen of Chlorophceite (No. 1583) is in an amygdaloidal
basalt from the Isle of Rum. This mineral appears to be a hydrated
basic silicate of iron, magnesium and calcium, derived from the
decomposition of the ferro-magesian silicates in the lavas, and
forming in their vesicular cavities an amorphous substance of dark
green, or in some cases almost black colour.

The series of Scottish minerals is brought to a close by a speci-
men of Chromite or chromic iron-ore (No. 1584) from Unst, one of
the Sheltand Islands, where it occurs in a matrix of serpentine.
This mineral, which is a member of the ' spinel group ' and is rather
variable in composition, has been worked commercially in Shetland
as a source of chromium and its compounds. The chromite
probably became segregated from a basic eruptive magma, through
which it was originally diffused.

DIVISION 2.
MINERALS OF IRELAND.

Minerals of Leinster.
(Nos. 1585 to 1600.)

The collection of Irish minerals, though not large, is fairly
representative, and gives within narrow limits a general notion of
the mineralogy of Ireland. According to Mr. H. J. Seymour,*
the number of mineral species known to occur in Ireland is abou
115.

In the arrangement of this Collection, the minerals of each of the
four provinces are grouped together. For a concise description of
the geology of Ireland, the visitor may be referred to the Guide to
the Survey Collections in the Dublin Museum of Science and Art.f

Among the minerals of Leinster the most interesting are the
specimens of Native Gold from Croghan Kinshelagh, in County
Wicklow (Nos. 1585 to 1587). This mountain is part of an elevated
tract rising to a height of 1987 feet above sea-level, and consisting
mainly of slaty rocks of Lower Silurian (Ordovician) age, associated

* " Preliminary List of the Minerals occurring in Ireland."- By Henry J.
Seymour, B.A. Rep. Brit. Asspc. t Belfast, 1902, p. 598. Also Supplementary
List in Rep. Brit. Assoc, Southport, 1903, p. 671.

t " Guide in the Collee lions of Rocks and Fossils belonging to the Geo-
logical Survey of Ireland " By A. MeHenry, M.R.I. A., and W. W. Watts,
M. A., Dublin, 1898

lvivi^-yn 'juli/.

with intruded masses of certain eruptive rocks. The gold occurred
in the valley gravel of several streams, principally in that of the
Gold Mines River.*

It has been suggested that the alluvial deposits of this district
probably supplied much of the gold used in the ancient Keltic
ornaments of Ireland. In modern times attention was prominently
directed to the Wicklow area by the accidental discovery of gold
there in the year 17'i.~>. Crowds of peasants were attracted to the
diggings, and it is said that gold to the value of several thousand
pounds was obtained by desultory working, before the Government
commenced systematic exploration. f The official workings were
discontinued at the outbreak of the Rebellion in 17'J*, but were
renewed in 1*01, when tunnels were driven into the mountain, in
quest of the quartz reels, which were supposed to have supplied
the detrital gold ; but these explorations were unattended with
success.

The largest nugget ever found in the Wicklow workings, repre-
sented by a model in Wall-case 14, reached the weight of about
22 ounces. Its remarkable story was told by the late Prof. V.
Ball. J Th e specimens in the Case under description include several
samples of the alluvial gold, of which No. l.jtf" is peculiarly interest-
ing, inasmuch as it shows the metal in a water- worn pebble of iron-
stained quartz, and consequently indicates the nature of the original
matrix.

The alluvial gold of Wicklow was associated with magnetite.
and to a less extent with cassiterite and wolfram, thus recalling the
conditions under which gold occurs in Cornwall. Other minerals
were also occasionally found, such as molybdenite, galena, chal-
copyrite, corundum, zircon and spinel, whilst the existence of
platinum, though not definitely proved, was suspected. § The origin
of the minerals was probably connected with the intrusion of the
eruptive rocks into the slates. [|

No. 15*8 is a specimen of granular magnetite from Ballycoog,
in County Wicklow, where workings were at one time carried on to
a limited extent upon vein.s of this mineral, coursing through
the slaty rocks of the district.

The mineral deposits of Wicklow, although yielding but little
at the present time, have been in their day more important than

* For the geological structure of the district, and for bibliography relating
to the Wicklow gold mines see " Explanatory Memoir to accompany sheets
138 and 139 of the Geological Survey of Ireland." By Edward Hull, LL.D.,
F.R.S. 1888.

f The workings formed the subject of a comic opera, played at Covent
Garden under the title of " The Lad o' the Hills ; or the Wicklow Gold Mines."

J " On the gold nuggets hitherto found in the County Wicklow." Sci.
Proc. Roy. Dublin Hoc. (new series, vol. viii. (1895), p. 311.

§ " On the Minerals of the Auriferous Districts of Wicklow." By William
Mallet, Esq. Jonr». Geol. ,W.. Dublin, vol. iv. (1851), p. i!<i!l.

| For the occurrence of Irish gold see paper by the late Gerrard A. Kin-
ahan " On the mode of occurrence and winning of gold in Ireland."- .Sci.
Proc. R. Dufj. Soc. (n.8.) vol hi. (188*), p. 2ti3.

^24 MINERALS OF IRfcL^:,^.

those of any other county in Ireland. The metalliferous minerals —
including ores of iron, copper and silver-lead — are confined chiefly
to a great band, or " mineral channel," stretching from Wicklow
in a south-westerly direction to Ovoca, and thence to Croghan
Kinshelagh, a distance of fourteen or fifteen miles.* The ore now
worked is for the most part iron-pyrites, known generally as Sulphur-
ore. Previously to about the year 1840 the pyritic deposits of Ovoca
were not worked for sake of their sulphur, but some of the ore-bodies
were wrought as copper-mines. Much of the pyrites, indeed, contains
a small proportion of copper, thus resembling the cupriferous
pyrites which occurs in enormous deposits in Spain and Portugal,
In recent years most of the Irish ore has been beaten out of the
market by Spanish pyrites. No. 1589 is a specimen of copper-
bearing pyrites from Ballymurtagh Mine, in the Vale of Ovoca.

In the year 1902 the mines of Wicklow yielded 1,617 tons of pyrites,
or " sulphur-ore," and 444 tons of cupreous pyrites, containing
about 2 per cent, of copper.

In addition to the copper in the iron pyrites, copper also occurs
to a limited extent, as chalcopyrite, forming distinct " bunches " of
ore : black copper ore, consisting chiefly of the oxide, was formerly
found in the shallow workings, sometimes in workable quantity,
and native copper was not unknown.

Large quantities of copper precipitate were formerly produced at
the Ovoca Mines, by means of scrap-iron which effected the reduction
of the metal from the coppery water that drained through the pyritic
deposits. The process was similar to that already noticed in
connection with the production of " cement copper " in Anglesea
(p. 127), An interesting historical account of the precipitation
processes, as carried on in Ireland and on the Continent, will be
found in the late Sir Warington Smyth's memoir on the mines of
Wicklow.f

Although no lead-ore is now worked in Wicklow, this mineral
was formerly the object of extensive exploration in certain parts
of the county. No. 1590 is a sample of galena crystallised on quartz,
from the old Luganure mines at Glendalough. The lodes yield-
ing the lead-ores of this district run through granite, in a
direction nearly north and south. Some of the other lead veins,
as at Glenmalure, occur near the junction of the granite with the
neighbouring mica-schist. A specimen of green pyromorphite
from Glenmalure is here shown (No. 1593), and there are also two
specimens of cerussite (Nos. 1591 and 1592), in further illustration
of the secondary ores of lead. Both specimens show the cerussite

* For a description of the metalliferous minerals of Ireland, see Mr. G. H.
Kinahan's comprehensive paper on " Irish Metal Mining " in Scient. Proc.
Roy. Dublin Soc, new series, vol. v. (1886), pp. 200-317.

t " On the mines of Wicklow and Waterford." Records of the School of
Mines, vol. i, part iii. (1S53), pp. 349-412. See also " Notes on the Recovery
of Copper from its solution in mine drainage, with special reference to the
Wicklow Mines." By Philip Argall and Gerrard A. Kinahan. Sc. Proc. Roy
Dub. Soc , new series, vol. iii. (1883), pp. 302-328.

MINERALS OF LEINSTER. t-'lM

in good crystals, and in No. 1592 these crystals are seated on a
matrix of decomposed galena, clearly suggesting the origin of the
carbonate as an alteration- product of the original ore.

Professor J. Joly has recorded the occurrence of harmotome
in the gangue of the Luganure lode, where also fluor-spar, barytes,
and strontianite occur, associated with galena, blende, pyrite and
copper pyrites.*

The mineral called KUmacooite, represented by No. 1505, is a
mixed sulphide, much resembling the so-called " blue-stone " of
Anglesea. It has been regarded as an intimate mixture of galena
and blende, and described by Dr. Tichborne as " an argentiferous
galenitic-blende." f It generally contains, however, not only
the sulphides of lead and zinc, but, also subordinately, and in
variable proportion, those of iron, copper and antimony, with silver
to the extent in some cases of eight ounces to the ton. Large
quantities of the mineral were raised from the Kilmacoo lode, in
the Connary Mine. According to Mr. Argall, the iron-pyrites in the
main lode at the Magpie Mine graduated locally into kilmacooite.t

The great mass of Leinster granite has yielded some interesting
minerals, but these are scarcely represented in this Collection. The
tray numbered 159(5 contains some beautiful crystals of transparent
quartz, of a delicate smoky tint, presenting the form which has led
to its name of Sceptre quartz. In such crystals, which are found near
Carlow, a slender six-sided prism is expanded towards the summit
so as to pass into a stouter prism, which is capped by the hexagonal
pyramid.

No. 1598 is an example of plumose mica, from near Dublin, showing
the silvery muscovite gracefully spread out in feather-like forms.

The mineral named Killinite, from Killiney Hill, south of Dublin,
where it was discovered in 1817, is represented by the specimen No.
1597. This mineral appears to have resulted from the alteration of
spodumene, a species which is known to occur in the granite.
According to the late Dr. Haughton " the so-called Killinite is an
altered spodumene. from which the lithia has been washed out by
weathering."§ It has long been known that Beryl occurs in the
Leinster granite, and it has been found by Prof. Joly in the
quarries of Glennullen, County Dublin. ||

*" On the occurrence of Harmotome at Glendalough, County Wicklow ■ "-
By J. Joly, B.E. 8c. P/oc. Roy. Dub. Hoc, new series, vol. v. (1886), p. 165.

t " On an argentiferous galenitic-blende at Ovoca."- By C. R. C. Tich-
borne, LL.D. Ibid., new series, vol. iv. (1885), p. 300.

% " Notes on the Ancient and Recent Mining operations in the East Ovoca
District." By P. H. Argall. Ibid., new series, vol. ii. (1880), p. 211.

§ " On the Mineralogy of the counties of Dublin and Wicklow." By the
Rev. Samuel Haughton, M.D. Jnnrn. Roy. 0<ol. 8oc. Ire/., new series, vol. v.,
part iii. (1880). p. 43.

See also Dr. Galbraith's paper " On the different analyses of Killinite. "-
.Joiirn. Oml. gnc. DvJ>., vol. vi. (lK.lfi), p. 165.

" Notes on the Minerals of the Dublin and Wicklow granite." By
J. Joly. B.E. 8c. Proc. Roy. Dub. 8oc, new series, vol. v. (1Ssi>), p. 48, 8ee
also Prof. J. P. O'Reilly in Journ. R. Oeol. Soc. Ird. (n.s.), vol. vii. (1887),
p. 69.

226 minerals op ireland.

Minerals of Connaught,
(Nos. 1599 to 1604.)

Among the ores which have been worked from time to'time in this
province, those of iron from the Connaught coalfield are perhaps the
most important ; but these ores are not at present represented in
the Collection.

Ores of lead and copper have occasionally been the object of ex-
ploration in Galway, where lodes and other ore-deposits occur in the
granitic and metamorphic rocks as well as in the Carboniferous
Limestone. No. 1599 is a specimen of copper-pyrites from the
Cregg Mine, in Oughterard. According to the Survey Memoir, by
Mr. G-. H. Kinahan, the mineral occurred in a strong lode bearing
N. 66° W. and hading to the south.* No. 1600 is a cleavage-piece of
galena, boldly crystalline in structure, from the neighbouring mine
of Clooshgereen, which was worked on a continuation of the Cregg
lode. Barytes occurs with the lead ore at the Cloosh Mine, and is
represented by two samples : in one of these, No. 1601, the mineral
forms a snow-white crystalline mass, and in the other, No. 1602, it
presents a translucent glassy appearance, with well-marked cleavage-
planes. The specimen No. 1602 was presented by H. E. A. Young,
Esq., whilst Nos. 1601 and 1602 were the gift of J. T. Darke, Esq,

In the year 1902 the province of Connaught yielded 463 tons of
barytes, but this was raised in County Sligo. Large deposits of
the mineral occur in the King's Mountain.

It is notable that Native Sulphur, quite a rare mineral in Britain,
occurs in the Carboniferous Limestone of Oughterard. No. 1603
is an excellent specimen of this sulphur, in its matrix, contributed by
the Geological Survey of Ireland. The sulphur occurs, in associa-
tion with calcite and pearl-spar, lining geodes or drusy cavities in
the limestone, and is occasionally found inside fossil shells. Mr.
Kinahan has suggested that the sulphur of Oughterard may have
been known in ancient times, since a river at this locality is named
Owenrift — a word which means in English " Brimstone River. "f

Native sulphur may owe its origin, in many cases, to reduction
from various sulphates, especially from gypsum, as already men-
tioned in connection with specimens from Nottinghamshire (p. 185).
It may also be reduced from metallic sulphides, like pyrites and
galena. Then again, natural waters, especially thermal springs, may
contain sulphides, from which sulphur will be precipitated on
exposure to the air, the deposition being facilitated by the action of
carbonic acid and by organic agencies like bacteria.

Among the few Connaught minerals here exhibited is a specimen
of Rutile (No. 1604) from the mica-schist of Cush-cum-Curragh,
near Borrishdale, on the north of Clew Bay in County Mayo. This

*Man. Geo!,. Sum. Ireland. Explanation of Sheet 105 and part of Sheet
114. By O. IT. Kinahan. 1869. p. 58.

f Mem. Oeol. Surv. Ireland. Explanation of Sheet 95. By G. H. Kinahan
and J. Nolan, 1870, p. 03.

Minerals of ulster. 227

specimen was presented by Spencer G. Perceval, Esq., by whom the
mineral was discovered at this locality in 1868. It occurs in
prismatic brown crystals, with vertical striations and other typical
characteristics. The mineral was analysed by Prof. Emerson
Reynolds, who noted the occurrence with it of small black crystals
of the variety of rutile distinguished as nigrine*

Minerals of Ulster.
(Nos. 1603 to 163:3.)

Several groups of minerals from different parts of the province of
Ulster are exhibited in this Division of the collection. One small
but interesting group represents certain minerals from the granitea
and crystalline schists of the highlands of Donegal. Among these
the specimens of Beryl are especially noteworthy. According to
Mr. R. H. Scott, f beryl occurs as an accessory mineral disseminated
through part of the granite as well as in veins of quartz running
along the joints. The large crystals of beryl exhibited here were
obtained from Sheskinaroan, a little to the north of Dungloe, on the
road to Anagary. One of the specimens, No. 1605, shows a six-sided
prism of opaque white colour, in a matrix of pegmatite ; whilst in
the tray, No. 1608, are two specimens of beryl, more or less greenish
in colour, and embedded in quartz. The Donegal beryl was analysed
by Dr. Haughton.J

By side of the beryls are exhibited several large crystals of
Garnet. The garnets of Donegal occur both in crystalline schists and
in altered limestone. The tray, No. 1609, contains two large brown
rhombic dodecahedra, more or less eroded on the surface, and
referable to the common species generally known as Andradite. Mr.
Scott refers to loose crystals, frequently two inches in diameter,
pitted by the action of sea-water, occurring on the beach at Tober-
keen. In No. 1610 the garnet is associated with Idocrase, or
Vesuvian, in brown bacillary forms. Such an association is by no
means uncommon, especially in the contact-zone between limestone
and crystalline rocks. Epidote and wollastonite occur in Donegal
under similar conditions. §

The minerals exhibited here from the highlands of Donegal were
obtained some forty years ago by Patrick Doran, a well-known
collector who visited the wildest parts of Ireland in quest of
minerals, and contributed materially to our knowledge of Irish
mineralogy. In addition to these there is a specimen of Cyanite
(No. 1611), from County Donegal, presented by J. Rhodes, Esq.

*" Note on Specimens of Rutile, from the County .Mayo." By J. Emerson
Reynolds. Journ. Roy. Oeol. Soc Dublin, new series, vol. ii. (1871), p. 164.

+ " On the Mineral Localities of Donegal."- Journ. Roy. Dub. Soc, vol. iv.
(1866), p. 114 ; Rep. Brit. Assoc, for 1863, p. 67.

i Quart. Journ. Oeol. fine, vol. xviii. (1862), p. 417 ; Rep. Brit. Assoc,
Newcastle-upon-Tyne, 1863, p. ~>S.

S For a geological description of N.W. and Centra! Donegal, see Mem.
Oeol. &■»>»■ Irel. to accompany Sheets 3, 4, ~>, 9, 10, 11, 1.3 and 16, 1891.

228 MINERALS OF TRELANi).

Another group of interesting minerals from a granitic district in
Ulster is illustrated by the specimens here exhibited from the Mourne
Mountains in County Down. This granite is especially interest-
ing to collectors of minerals inasmuch as it presents in marked degree
a miarolibic structure, that is — it contains numerous cavities which
are lined with crystals of the constituent minerals. It is from these
druses that the specimens here exhibited have been obtained.
According to Prof. Sollas the granite of the Mourne Mountains is in
all probability of Tertiary age* — a view supported by other
geologists.

In No. 1612 a drusy cavity contains rather large crystals of
orthoclase associated with sharply defined crystals of smoky quartz,
and with a dark mica. The granite of the Mourne Mountains
contains also albite, or soda-felspar, as first pointed out by Dr.
Haughton. In some of this granite the quartz, contrary to its
usual habit, has consolidated before the felspar.

Among the accessory minerals of the granite, topaz and beryl
occasionally occur as crystals studding the walls of the cavities.
A beautiful crystal of colourless Topaz, of characteristic prismatic
habit, is seen in No. 1616 ; whilst excellent crystals of Beryl will be
found in the trays, Nos. 1613, 1614 and 1615. One of the
beryls presents the form of a rather clear green prism, without the
terminal plane ; in another specimen the sea-green crystal shows
the hexagonal prism combined with the basal pinacoid ; whilst in
a third specimen the prismatic crystal is opaque and fractured.
The Irish beryls are further represented by three isolated crystals of
blue colour, sufficiently clear to be cut as ornamental stones. These
are in the tray, No. 1615. One of these is a magnificent crystal,
presenting the form of a striated six-sided prism measuring two
inches in length, translucent and bright blue at one end, but be-
coming white, dull and opaque towards the base. The basal plane
is rough and is coated with a little oxide of iron. Transparent beryl,
when of a bluish-green colour is known as Aquamarine.

A special group of minerals is yielded by the Tertiary volcanic
rocks of the north-east of Ireland. These rocks are mostly basalts
and dolerites, in many cases amygdaloidal, and containing zeolitic
minerals of much beauty, closely resembling those of the Western
Isles of Scotland. Prominent among the zeolites here exhibited are
the specimens of Analcite or analcime (Nos. 1617 to 1619), mostly in
dead white icositetrahedral crystals. In the specimen. No. 1619,
however, the little sharply defined crystals are translucent or trans-
parent, and are seated on " wacke," or decomposed trap-rock, from
Benyevenagh. " It is an interesting fact," wrote Colonel Portlock
in reference to the Irish analcime, " that the transparent varieties
are invariably of a lower degree of hardness than the more opaque. "-j-

* " Preliminary Observations on the Granites of Wicklow and Down."
Srien. Proc. Hoy. Dub. Sac, new series, vol. vi. (1888), p. 257.

t " Report on the Geology of the County of Londonderry, and of parts of
Tyrone and Fermanagh." Dublin, 18 13, p. 220.

MINERALS OF ANTRIM. 229

One of the commonest of the Ulster zeolites io Xatrolitr. (Mob. 1021,
1622) — a mineral which usually occurs in delicate white needle-like
crystals, shooting across the cavities of the vesicular lava. Among
the other so-called " basaltic minerals " mention may be made of
Antritnolite (No. 1(525) one of Dr. Thomson's numerous " species "
now regarded as a variety of mesolite. The specimen shows the
antrimolite from the Giant's Causeway in white botryoidal masses,
of radio-fibrous structure. The Levyne (No. 1620), named by Sir
D. Brewster after Levy who made the catalogue of the Turner
collection, seems to be a variety of chabazite, though much dis-
cussion has arisen with regard to its true relationship. Gyrolite, of
which No. 1623 is a specimen, is a zeolite regarded by some as an
altered form of apophyllite.

The dark green mineral in the basalt, No. 1626, is Thomson's
Kirwanite — a mineral which has perhaps resulted from the decom-
position, of the augitic constituent of the rock, and seems to be re-
lated to the group of rather ill-defined substances known as " green
earth."

No. 1627 is a specimen of basalt from the Isle of Muck, near
Magee Island, off the east coast of Antrim, showing well-defined
octahedral crystals of magnetite coated with brown oxide of iron.
Even larger octahedra are seen on the fine specimen from Magee
Island, No. 1628.

At the present day the iron-ores of Antrim are the most important
minerals raised in Ireland. * In the year 1902 the county yielded
as much as 81,612 tons of ore. The " iron-ore measures " are an
irregular series of iron oxides with clays and lignites, associated
with volcanic tuffs, intercalated between the upper and lower
groups of basalts and dolerites. Thin beds of bole, or ferruginous
clay, resulting from the atmospheric disintegration of the volcanic
rocks, occur between the successive lava flows at various horizons,
especially in the Lower Basalts, but the great group of iron-bearing
minerals, with the associated lignites and clays, forms a definite
zone, probably of lacustrine origin, representing deposits in sheets
of shallow water on the exposed surface of the older set of lava-
flows. The richest ore is known from its structure, as pisolitic iron-
ore, or pebble ore (No. 1629).f This is composed of small concretions
of limonite or haematite, embedded in a matrix of ochreous clay.
Somewhat similar concretionary ores are in course of formation at
the present day at the bottom of certain lakes, especially in Sweden,

* See Mem. Geol. Surv. Explanatory Memoir, Sheets 21, 28 and 29 (Ire-
land). By Edward Hull, M.A., P.R.S. (1876.) Also, Sheet 20. By R.
Glascott Symes, M.A. (1886), and Sheet 19. By R. G. Symes and Alexander
McHenry (1886).

fSee " Notes on some of the Irish Crystalline Iron-Ores." By G. H. Kinahan.
8c. Proc. Roy. Dubl. Soc, new series, vol. iv. (18S5), p. 306 ; also " Notes on
the Tertiary Iron-Ore Measures, Glenariff Valley, County Antrim."- By
Philip Argall. Journ. Roy. Geol. Soc, Ireland, hew series, vol. vi. (1886), p.
98 ; and in Sc. Proc. Roy. Dublin Soc, new series, vol. iii. (1883), p. 151 .

230 MINERALS OF IRELAND.

where the deposition of the iron-oxide seems to be determined by
the play of organic activities, whilst the ultimate source of the iron
is probably referable to the decomposition of pyrites or of various
iron-silicates in the crystalline rocks.

In the substance known as Belfast aluminous ore (No. 1630) the
oxide of iron is associated with much alumina uncombined with
silica, and the substance has thus acquired value as a fluxing agent
in the reduction of siliceous ores, like certain kinds of haematite. It
is sometimes regarded as a kind of bole. Aluminium hydroxide, in
which iron replaces aluminium to a greater or less extent, is often
termed Bauxite, from Les Beaux, a locality near Tarascon in the
south of France ; but the name has been used rather loosely and
extended to various mineral substances, some of which pass into
ferruginous clays. Bauxite is used in the preparation of aluminium
and its salts. In the year 1902 the Irish bauxite (No. 1631) was
raised to the extent of 9,047 tons. Alumina is prepared from this
material at the works near Lame, and is sent thence to Foyers, in
Inverness-shire, where it is reduced to the. metallic state in the
electric furnace.* Some of the so-called bauxite of Antrim has
been known as alum clay, but the proportion of silica is sometimes
extremely low. Titanic oxide exists, however, to the extent of
about 2 per cent. ,No. 1632 is a sample of the ferriferous clay known
as lithomarge, which occurs with the iron-ore measures, and here
presents the appearance of a speckled purple rock. The " pavement "
is the name given locally to a poor kind of ore, on which the richer
ore rests. At the Evishnably Mine the pisolitic ore yielded 35 to 40
per cent, of iron ; the pavement about 28 per cent, and the violet
lithomarge about 17 per cent.t

On the evidence of the vegetable remains preserved in certain leaf -
beds between the Upper and the Lower basalts, it is inferred that the
volcanic outbursts in the Antrim plateau go back to Oligocene or
even to late Eocene time. The iron-ore measures seem to
represent the denudation of the volcanic rocks during a pro-
longed pause between the earlier and the later episodes of volcanic
activity.

Superficial deposits of bog iron-ore are found in various parts of
Ulster, and the substance has in some cases been worked for use in
the purification of coal-gas. The ore is an impure limonite,
formed partly by organic agency.

Strata of Triassic age occur in County Antrim, and here as else-
where the Keuper marls contain rock salt and gypsum. No. 1633
is a specimen of clear colourless crystalline salt, or Halite, from
Maiden Mount Mine, near Carrickfergus. It appears that salt
was first discovered in Antrim, while sinking for coal in 1850. At
the present time the salt-measures are rather extensively worked

* " Mineral Statistics " for 1902, p. 172.

f Mem. Oeol. Surv. Memoir to accompany Sheet 20, Ireland. By R,
Glascott Symes, M.A. (1886), p. 12.

VTXETt U.S OF MPNSTETi.

in the neighbourhood of Carrickfer^u5. + In the year l'J02 the county
of Antrim yielded 32,52'J tons of rock-salt, and 12,063 ton.s of salt
from brine-springs.

Minerals of Munster.
(Nos. 1634 to 1644.)

It is probable that the earliest workings for metalliferous minerals
in the province of Munster were those in the copper deposits of the
Knockmahon district, on the coast of Waterford. In this locality
the '" old men's workings " have yielded rude implements of stone
and wood, pointing to mining operations at a remote period. The
ores occur in lodes running through Lower Silurian (Ordovician)
strata, associated with igneous rocks. No. 1634 is a sample of
copper-pyrites from Knockmahon. The lodes yielding the copper
also frequently carried silver-lead ores.f

Ores of cobalt have occasionally been found in association with
the copper-ores of Waterford, and the specimen, Xo. 1635, from
Bonmahon Head, shows the erythrite, or cobalt-bloom, in company
with an incrustation of malachite ; the characteristic pinkish tint
of the former strikingly contrasting with the green colour of the
latter.

Another group of copper-ores is represented by Nos. 1G41 and
1642, from the south-western part of County Cork. Although the
minerals are rather widely distributed throughout this district,
it is only in a few localities that they have been found in sufficient
quantity to be profitably worked. The Bearhaven or Allihies
Mines, which at one time were extremely productive, are situated
in a secluded part of the promontory between Kenmare and Bantry
Bays. The ores occur in quartz-lodes coursing through killas,
near the junction of what is often regarded as the Upper and the
Lower Old Red Sandstone.]: No. 1636 is a sample of copper-pyrites
from Bearhaven, whilst No. 1637 is a specimen of eruhescite, or purple
copper-ore, from Ballycummisk Mine, near Skull.

Lead-ores, associated to some extent with the ores of zinc and
copper, occur in the Carboniferous Limestone of County Clare. The
specimen of coarsely crystalline galena, curiously striped, No. 1038,
is from a pocket in the limestone at Ballyhicky Mine. An interesting
mineral found in the Carboniferous rocks of Kilbrickan or Monanoe,
in County Clare, was described by Dr. Apjohn as far back as 1840,

*"The Salt Industry of Carrickfergus." By A. Miscampbell. Trans.
Fed. Inst., vol. vii. (1894), p. 546.

t Mem. Geol. Surv. Explanation of Sheets 167, 168, 178, and 179. By
G. V. Du Noyer, 1865.

% Ibid. Explanation of Sheets 197 and 198 (1860). Notes on the mines
by Warington Smyth, M.A., P.R.S., p. 30. Also Explanation of Sheets
200, etc., 1861.

232 MINERALS OF IRELAND ANT) ISLE OF MAN.

under the name of Kilbrickanite (No. 1639). This is a sulph-anti-
morrite of lead which has been recently shown by Mr. G. T. Prior s
analysis to be identical with the species geocronite. This analysis
revealed the presence of arsenic to the extent of 4-59 per cent.*

From a quarry of Carboniferous Limestone at Eockf orest in County
Cork, was obtained some years ago, the beautiful mineral which
Prof. Harkness named Cotterite, in compliment to Miss Cotter
through whom it was procured. A specimen is here exhibited, as
No. 1640. This mineral is a variety of quartz, remarkable for its
peculiar silvery lustre, associated with a pearly sheen. The cotterite
forms thin laminae, coating pyramidal quartz, and enclosing delicate
films of limonite between the laminae. It occurred in a quartz
vein, covered by a thin layer of fine reddish clay, and Harkness
suggested that the clay had yielded silica which was deposited on
the quartz in a laminated form, the delicate lamination being
responsible for the peculiar lustre. f

The series of Irish minerals is brought to a conclusion by several
fine specimens of Wavellite (Nos. 1641 to 1644), from Clonmel in
County Tipperary. These are beautiful mammillary masses of
fibrous structure, displaying on fracture a radiate formation recalling
that of the well-known wavellite of Devonshire, but on a rather
bolder scale. Wavellite occurs likewise in the Lower Carboni-
ferous rocks of Co. Cork.

MINEEALS OF THE ISLE OF MAN.
(Nos. 1645 to 1652.)

A few specimens placed at the end of the collection serve to
represent, though imperfectly, the minerals of the Isle of Man.
The mineral resources of the Island have been fully described by
Mr. G. W. Lamplugh in his comprehensive official memoir,J a
memoir in which he has given an historical account of local mining, §
and has added a list of all the minerals, comprising upwards of
seventy species, known to occur in the island, whether in lodes or as
rock-constituents . 1 1

By far the most important minerals, from an economic point of
view, are the ores of lead and zinc. The sample of galena, No. 1645,
represents the lead-ore of the famous Foxdale Mine. Here, the lode,
or system of lodes, runs in a direction almost due east and west
for a distance of between two and three miles, and has been worked
down to a depth of nearly 2,000 feet. The vein passes from the
Manx slates into granite, and it is notable that although it is equally

* " The Identity of Kilbrickanite with Geocronite." Min. Mag., vol xiii
(1902), p. 186.

-j- " On Cotterite, a new variety of Quartz." By Prof Harkness. Min
Mag., vol. ii. (1878), p. 82.

% Mem. Oeol. Surv. " The Geology of the Isle of Man." (1903.)

§ Op. cit., p. 480.

|| Op. cit. p. 572.

MINERALS OT? TST,E OF MAN. 233

productive in both typo-, of " country," the galena in the slate
or killas, is found to lie richer in silver than that in the granite. In
the specimen, No. 1015, which came from the Townsend Mine at
Foxdale, and was presented by Capt. W. Kitto, the galena is
crystallised in cubo-octahedra. In the specimen of Polytdite,
or argentiferous fahl-ore, No. 1(316, the proportion of silver, accord-
ing to Mr. David Forbes, amounted to 13-57 per cent* This
mineral was found in the easterly workings at Foxdale, where the
lode passes into a granite country.

Another interesting mineral from the Foxdale Mines is the
Plumosite, or " feather-ore," of which No. 1017 is an excellent
example. This rare mineral was described by Sir Warington
Smyth, at the time of its discovery, about 1880.f It occurred in
association with fine-grained galena and with vuggy or cellular
quartz. The plumosite somewhat resembles cotton-wool, of dark
colour, and consists of a felted mass of bright grey metallic hairs. It
is a sulph-antimonite of lead, which may be regarded as a capillary
variety of jamesonite. According to Capt. Kitto, the plumosite
occurred only in the neighbourhood of galena that was rich in silver.

In the year 1902 the Foxdale Mines yielded 4,192 tons of lead-ore,
from which (32, OX) ounces of silver were obtainable. A large
specimen of galena, in aggregated cubo-octahedra, associated with
blende and dolomite, from the Laxey Mines, will be found in the
lower part of the pedestal case, on the opposite side of the Museum,
near Section Q of the Horse-shoe Case. This huge specimen was pre-
sented from the Great Exhibition of 1851.

Rich silver-lead ore was formerly raised at the famous Laxey
Mines, and at one time copper-ore was produced there, but the work-
ings at present are directed to the extraction of the ores of zinc. Nos.
1648. 1649, are samples of the blende of Great Laxey. The ores occur
in a lode of very variable width, coursing in a north-and-south
direction through slaty flags, of the Manx slate series. The chief
minerals are blende and galena, in a gangue consisting mainly of
quartz and calcite. In the Wall-case No. 12, on the opposite side of
the room, are some very fine specimens of blende, with crystallised
quartz, from the Laxey Mines, presented by Capt. Rowe. In the
year 1902, Great Laxey yielded 963 tons of blende ; whilst about
the same amount was obtained from Snaefell Mine, situated three
miles N.W. of the village of Laxey.

Very curious globular masses of radiated blende were yielded at
one time by the Townsend or Cornelly Mine — a mine established on
an east-and-west lode parallel to that of Foxdale. One of these
spheroidal masses, presented in 1878 by Capt. Kitto, is exhibited in
Wall-case 28. The specimen is broken across in order to display the
radiate structure of the blende, and to expose the central mass of
quartz and copper-pyrites.

* •' Researches in Britirfi Mineralogy." Phil. Mag., 4 ser., vol. xxxiv.
(1867), p. 329.
f Trans. R. Geol. Soc, Corn., vol. x. (1887). p. 8A

7882. H

234 MIXEKALS OK THF. TSLE OF MAN.

Iu tlie specimen, No. 1650, from Laxey, crystals of cupper-pyrites
are seated on the eroded surface of a large rhombic dodecahedron of
zinc blende. A very handsome specimen, of similar character, will
be found in Wall-case 12. In No. 1651, also from Laxey, the copper-
pyrites is crystallised on well-defined rhombohedra of dolomite.
The latter mineral is by no means uncommon in some of the Manx
lodes, and remarkably fine crystals occasionally occur. Copper-ore
is found in subordinate quantity in many of the mineral- veins, but
the most notable occurrence was at the old Bradda Mines, where
the copper-pyrites was associated, as at most of the other localities,
with argentiferous galena. The lode, forming a conspicuous feature
in the fine cliffs of dark slaty rocks at Bradda Head, was regarded by
Sir Warington Smyth as '' the noblest surface exhibition of a
mineral vein to be seen in Europe."

In discussing the origin of the metalliferous deposits in the Isle of
Man, Mr. Lamplugh is disposed to connect them with the volcanic
activity of the Tertiary period, suggesting that the fissures through
which the igneous material of the dykes was brought up may have
served also as conduits for the vapours and solutions which deposited
the mineral matter of the lodes.

Hcematite has been worked in the neighbourhood of Manghold Head,
in the north of the island, where the ore occurs in bold veins coursing
through the slaty rocks of the cliffs. The source of the haematite
may probably be referred, as Mr. Lamplugh suggests, to the New
Red strata which are believed to have formerly overlapped the
slates.

The specimen, No. 1652, presented by Sir W. W. Smyth, in 1861,
is a representative of the anthracite, which was found, at that time,
in the Laxey Mines. This specimen was obtained from a depth of
110 fathoms. Unfortunately, the exact mode of its occurrence has
not been recorded, and it remains doubtful whether it occurred as a
constituent of the lode, or was derived from the adjacent slate. If
really a vein-mineral, as some authorities have held, its origin may
have been similar to that of certain graphitic substances that appear
to have no relation with altered vegetable matter. The occurrence
of graphite, in very limited quantity, has been recorded from the
Snaefell lode and from Beary Mountain, in the heart of the Isle of
Man. For a brief notice of the probable mode of formation of
graphite, reference may be made to p. 160.

INDEX.

Actinium, so.
Actinolite, 101.
Adipoeere, mineral, 121.
Aerated Baryte-s 170.
Aetites, 194.
Agate, 218.
Alabaster, 182.
AUute, 100.
Alcohol (galena) 137.
Allophane, Devon, 103.

Kent, 200.

Alluvial Tin-ore, 18.
Almandine, 100.
Alquifoux, 137.
Alstonite, 171.

Alston Moor, minerals of, Hil.
Alum clay, 230.
Aluminite, 201.
Aluminous iron-ore, 23o.
Amber, 203.
Amethyst, 92.

Analcite (analcime) 217, 221, 228.
Anatase, 100, 128, 191.
Andradite, 101.
Andrewsite, 53.
Anglesite, Anglesea, 127.
Derbyshire, 139.

Leadhills, 207.

Anhydrite, 185.
Anthracite, 234.
Antimonite, 59.
Antimony glance, 59.

ores, 59.

Antrim iron-ores, 229.
Antrimolite, 229.
Apatelite, 197.
Apatite, Cornwall, 23.

Cumberland, 153.

Apochromatic lenses, «7.
Aquamarine, 228.

Aragonite, Cumberland, 149, 172.

Devon, 98.

■ Leadhills, 210.

Argentite, 50.
Arsenic, 32.
Arsenical mundic, 31.

pyrites, 31.

Asbestos, 129.

Asbolan, 125, 190.

Asphalt, 178, 179.

Associates of Cassiterite, 19, 21.

Atacamite, 49.

Aurichalite, Cumberland, 158, 167

Leadhills, 209.

Autunit'-, K3.
Axinite, 30.
Azurite, 40, 105, 190.

Babel iiuartz, 91.

Bagsliot sands, 29.

Balls, ironstone, 119.

Barite, 168.

Barium in natural waters 187.

Barytes, Cornwall, 95

Cumberland, 151, 168.

— Derbyshire, 135.

in London Clay, 188.

in Lower Greensand, 18*.

in Trias, 186.

Barytocalcite, 171.
Barytocelestite (barytocelestinel,

115.
Bauxite 230.
Baylilonite, 53.
Beef (calcite), 202.
Beekite, 97.
Bell-metal ore, 20.
Beryl, Donegal, 227.

Leinster, 225.

Mourne Mountains, 228.

Scotland, 220.

Bindheimite, 59.
Bismite, 79.
Bismuth, native, 7 m.

glance, 79.

ochre, 79.

ores, 7h.

Bismuthinite, 79.
Bismuthite, 79-
Bitumen, Elastic,
Black cawk, 160.

copper-ore, 38,

Jack, 141.

lead, 1 59.

muck, 145.

oxide of manganese, '1

pyrites, 119.

Blackband ironstone, 119.
Blast ore, 144.
Bleierde, 13k.
Bleinieritc, 59.
Blende, Cornwall, 58.

Cumberland, 165.

Derbyshire, 140.

Isle of Man, 233.

Wales, 124

hexagonal, 214.

ruby, 124.

Blister copper-ore, 36.
Bloodstone, 144.
Blue iron-earth, 71.

John, 135.

lead-ore, 55.

stone, 127.

vitriol, 46.

134.

44.

236

jNDEa.

Bogiron-ore, 193, 230.

Bornite, 39.

Botallackite, 49.

Bournonite, 62.

Boxes (pseudomorphs), 69.

Brass ore 158.

Brasses, 119.

Brendon Hills, iron-ores, 105.

Brewsterite, 211.

Bristol diamonds, 113.

minerals of, 112.

Brochantite, 158.
Bromlite, 171.
Bronze, 8.
Brookite, 128.
Brown iron-ores, 193.

lead-ore, 155.

Brush ore, 116.

Bull beef (fluor), 135.

Buntkupfererz, 39.

Butterfly twins (calcjte), 132, 149.

Buttons of galena, 163.

Buxton diamonds, 136.

Cairngorm, 220.

Calamine, Cumberland, 166.

Derbyshire, 141.

Mendips, 109.

pseudomorphs, 141.

Calcite, Cornwall, 93.

Cumberland, 149, 172.

Derbyshire, 132.

Devon, 98.

North Wales, 124.

Strontian, 210.

Calco-uranite, 82.

Caldbeck Fells, minerals of, 152.

Caledonite, 208.

Campylite, 156.

Cann (fluor), 86.

Caoutchouc, mineral, 134.

Capels, 11, 28.

Capped quartz, 91.

Carlsbad twins, 14, 99.

Cassiterite, Cornwall, 8, 15.

Ross-shire, 220.

Wicklow, 223.

Cawk, 136.

Cela.donite, 218.

Celestite (celestine), 113, 186.

Cellular quartz, 177.

Cement copper, 44, 127, 224.

Cerargyrite, 58.

Cerussite, Cornwall, 56.

Cumberland, 165.

Derbyshire, 138.

Devon, 56.

Leadhills, -207.

Chabazite, 217,221.
Chalcanthite, 46.
Chalcedony, 96, 200.
Chalcocite, 37.
Chalcolite, 83.
Chalcophyllite, 53.

Chalcopyrite, 35.
Chalcosiderite. 54.
Chalcotriehite, 42.
Chalybite, Cornwall, 69

Devon, 69.

Durham, 167.

Somersetshire, 105

Chamoisite, 192.
Chenevixite, 53.
Chessylite, 46, 105.
Chiastolite, 159.
Childrenite, 71.
Chloanthite, 75.
Chlor-apatite, 23.
Chlorite, 101.
Chloropal, 104.
Chlorophaeite, 222.
Chlorophane, 88.
Chromite, 222.
Chrysocolla, 46.
Churchite, 83.
Clay iron-stone, 119.
Cleveland ore, 191.
Cinoclase, 52.
Clod (iron-marl), 116.
Cluthalite, 217.
Cobalt bloom, 76, 231.
Cobalt ores, Cornwall 75.

Ireland, 231.

Cock's-comb barytes, 168.

pyrites, 142.

Cog-wheel ore, 63.
Coke (calamine), 125.
Comby lodes, 21.
Condurrite, 64.
Connaught, minerals of, 226.
Connellite, 48.
Copaline, 203.
Copiapite, 197.
Copper mica, 53.
Copper, native 44, 213.
Copper ore, black 44.

, red 42.

vitreous 37.

Copper-ores, Cheshire, 189.

Cornwall, 33.

— Devon 33.

Ecton 142.

Ireland, 224, 231.

Leadhills, 209.

— N. Wales, 126.
Copper precipitate, 127, 224.

pyrites, 35.

shale, 189.

uranite, 82.

Cornish diamonds, 91.
Cornwall, minerals of 5.
Cornwallite, 52.
Cotterite, 232.
Country (minor's term), 7.
Coveliitc, 38.
Crease, 116.
Crested barytes, 168.
Crocalite, 217.

INDEX.

237

< romfordite, 139.

Cronstedtite, 73.

Cross course^, 7, 54.

Cross-course spar, 91.

C'rustification, 21.

Cube ore, 72.

Cumberland minerals, 143, 152, 161.

Cupreous Calamine, 158.

Cuprite, 42.

Cupro-uranite, s2.

Cyanite, 227.

Cyanosite, 46.

Dean Forest, minerals of, 116.

Delessite, 218.

Derby shirt-, minerals of, 131, 137.

Desmine, 217.

Dt-villine, 47.

Devon, minerals of, 5.

Devonshire sand, 67.

Diallage, 103.

Dialogite, 77, 120.

Diamonds, Bristol, 113.

Buxton, 136.

Cornish, 91.

Merthyr, 121.

Dogs (pyrites), 117.
Dog-tooth spar, 132.
Dolomite, Cornwall, 94.

Cumberland, 149, 173.

' Isle of Man, 234.

S. Wales, UK.

Dolomitic conglomerate, 111.
Dripstone, 133.
Druses, 65.
Dufreynite, 71.

Eagle-stones, 194.

Ecton minerals, 142

Edingtonite, 218.

Eisenkie-el, 92, 113.

Elastic bitumen, 134.

Elaterite, 134

Electric Calamine 1 59.

Electrum, 130.

Elven, 7.

Endellioniti-, 63.

Enysite, 48.

Epidote, 159.

Epimorphs, 1 .

Erubeseite, 39.

Erythrite (erythrine), 76, 231.

Exnioor iron-ore^, 106.

Eyam twins, calcite, 132.

Eye agate, 219.

Fahl-ore (Fahlerz), 64.

False lead, 141.

Felspar, 99

Felspar, kaoliniaation of, 10.

Ferberite, 153.

Fire-stone. 199.

Flats, 132, 162.

Flint, 200.

Float-ore, 162.
Flos ferri, 172.
Fluellite, 26.

Fluor (fluorite or Huor-.-par), Corn-
wall, 26, 85.

Cumberland, 174.

Derbyshire, 134.

Devon, 86.

X. Wales, 124.

Fluor-apatite, 23.
Fluorescence, 175.
Fluoroid, 86.

Forest of Dean, minerals of, 116.
Fossils, old use of wood, 5.
Fossil " oak" (barytes), 136.
Francolite, 24.
Fumaroles, 31.

Galactite, 217.
Galena, Cornwall, 55.

Cumberland, 162.

Derbyshire, 137.

Devon, 55.

Isle of Man, 232.

Leadhills, 206.

Mendips, 108.

Strontian, 210.

Wales, 118, 122, 123.

Gallium, in Cleveland ore, 192.
Gangue, 84.

Garnets, Cornwall, 100.

Cumberland, 159.

Donegal, 227.

Gas, natural, 204.
Geodes, 65.
Gilbertite, 27.
Glauconite, 195.
Goethite, 68.
Gold, Cornwall, lb.

Ireland, 222.

Scotland, 205.

Wales, 129.

Goslarite, 139.
Gozzan (gossan), 41.
Graphite. Cornwall, 104,

Cumberland, 159.

Isle of Man, 234.

Gravel ore, 123.
Green lead-ore, 15:,.

linnets, 139.

Greisen, 11.

Grey antimony-ore, 59.

copper-ore, 3K, 64.

iron-ore, 116.

manganese-ore, 77.

Groovers, 108.

Grossularia, 81.

Gruenlingite, 154.

Gypsum, in Purbeck beds, 1K5.

in Trias, 182.

Gyrolite, 222, 229.

Hacked quartz, 91.
Haematite, Cornwall, 67.

>oS

index.

Haematite, Cumberland, 144.

N. Wales, 125.

— - S. Wales, 117.
Hair- pyrites, 120.
Halite, Cheshire, 181.

Ireland, 230.

Halloysite, 103.

Hard-spar (quartz), 90.

Harmotome, 211.

Hatchettine, 121.

Hay tori te, 97.

Health- stones, 198.

Heart-shaped calcite, 132, 149.

Heavy spar, 168.

Helium, 80.

Hemimorphite, Cumberland, 158.

Leadhills, 209.

Henwoodite, 54.

Hepatic alteration of pyrites, 197.

Heulandite, 217.

Hexagonal blende, 214.

Highgate resin, 203.

Highlands of Scotland, minerals

of, 219.
Hitchcockite, 156.
Horn silver, 58.
Homstone, 97.
Horse-flesh ore, 39.
Huebnerite, 153.
Huel, 13.
Hydrargyllite, 99.
Hydro-haematite, 147.
Hydro-micas, 101.

Idocrase, 227.

Indigo copper, 39.

Ireland, minerals of, 222.

Iron bloom, 173.

iron glance, 147.

Iron ores, Brendon Hills, 105.

Bristol, 112.

Cornwall, 65.

Cumberland, 143.

— Devon, 65.

Forest of Dean, 116.

Jurassic, 191.

Mendips, 110.

• Northamptonshire, 192.

Yorkshire, 191.

Weald, 193.

Iron Pyrites, Cornwall, 60.

Cumberland, 167.

Derbyshire, 142.

Wicklow,_ 224.

in Neozoic Strata, 196.

Iron-quartz, 92, 113.
Ironstone, clay, 119.
Iserine, 67.
Isle of Man, minerals of, 232.

Jamesonite, 59.
Jasper, 129, 219.
Jet, 202.
Jews'-house tin, 7,

17.

Joseite, 155.

Jurassic iron-ores, 191,192.

Kilbrickanite, 232.
Killas, 7.
Killinite, 225.
Kilmacooite, 225.
Kirwanite, 229.
Kwh, 160.
Kupfernickel, 75.
Kupferschiefer, 189.

Lake iron-ores, 229.
Lanarkite, 207.
Lancashire, haematite of, 143.
Langite, 47.

Lapis Calaminaris, 109.
Lateral secretion theory, 14.
Laumontite, 217, 221.
Lead-earth, 138.
Lead-glance, 137.
Lead-ores, Cornwall, 54.

Cumberland, 161.

Derbyshire, 137.

Devon, 54.

Isle of Man, 232.

Leadhills, 206.

Mendips, 107.

Shropshire, 177.

Strontian, 210.

Triassic, 120.

Wales, Mid., 122.

Wales, N., 123.

Wales, S., 118.

Leader, 10

Leadhillite, Mendips, 108,

Scotland 208.

Leadhills, minerals of, 205.
Leicestershire, minerals of, 178
Leinster, minerals of, 222.
Lepastrum, 188.
Lepidocrocite, 148.
Lepidolite, 27.
Levyne, 229.
Liassic iron-ores, 191.
Libethenite, 51.
Lime-uranite, 82.
Limnite, 195.
Limonite, 68, 117, 194.
Linarite, Cumberland 157.
— — Leadhills, 208.
Linnets, 139.
Liroconite, 52.
Lithia mica, 27.
Lithomarge, 103, 230.
Lodes, 6.
Loughs, 147.
Ludlamite, 71.
Lunnite, 52.
Luxullianite, 29.
Lyellite, 47.

Magnesite, 102.

i \ t dex .

2?fi

Magnetic i>y rites, 168.

Magnetite, Cornwall, 66

Devon, 66.

Ireland, 221).

Yorkshire, 1112.

Malachite 46, 105, 157.

Malleable copper, 44.

Man, Isle of, minerals of, 232.

Manganese nodules, 126.

Manganese-ores, Cornwall, 70.

Devon, 76.

N. Wales, 125.

Manganese-Spar, 77.

Manganite, 77.

Marcasite, 198.

Marmatite, 58.

Martite, 66.

Matlockite, 139.

Melaconite, 43.

Melanterite, 197.

Menaccanite, 67.

Mendip Hills, minerals of, 107.

Mendipite, 108.

Merthyr diamonds, 121.

Mesolite, 217, 222, 229.

Metalliferous slates, Wales, 121.

Mexico, Huel, 57.

Miarolitic structure, 228.

Mica, 27.

Micaceous iron-ore, 67.

Midland Valley, Scotland, minerals

of, 213.
Mid-Wales, minerals of, 121.
Milky quartz, 129.
Millerite, 120.
Mimetite, Cornwall, 56.

Cumberland, 156.

Mineral adipocere, 121.

caoutchouc, 134.

Minette, 192.

Minium, native, 206.

Mispickel, 31, 62.

Mock-ore, 141.

Molybdenite, 154, 179.

Molybdic ochre, 154.

Molybdite, 154.

Monazite, 100.

Moonstone, 183.

Morvenite, 212.

Moss agate, 219.

Mother of lead, 163.

Mottramite, 191.

Mourne Mountains, minerals of,

228._
Mundic, 60.

Arsenical, 31.

Munster, minerals of, 231.
Murchisonite, loO.

Nail-headed calcite, 172.

copper-ore, 37.

Native bismuth, 78.

copper, 44, 213.

~— gold, 18, 129, 205, 222.

Native silver, 57.

sulphur, 226.

Natrolite, 217, 229.
Natural gas, 204.
Needle iron-ore, 68.

tinstone, 16.

Neozoic strata, 180.
Niccolite, 75.
Nickel, 120.

ores, Cornish, 75.

pyrites, 120.

Nigrine, 227.

North Wales, minerals of, 1 23.

Northampton iron-ore, 192.

Ochre, 111.
Olivenite, 51.
Onyx, 219.
Onyx barytes, 136.

marble, 173.

Oolitic iron-ores, 191.
Opal, 97.
Orthoclase, 99.

Paragenesis, 19.

Passyite, 199.

Peach, 101.

Peacock copper-ore, 36.

Pearl spar, Cornwall, 94.

-, Cumberland, 149.

Pebble iron-ore, 229.

Pebbles, Scotch, 218.

Pectolite, 218, 222.

Pencil-ore, 144.

Pentlandite, 75.

Penwithite, 78.

Pharmacosiderite, 72.

Phillipsite, 39.

Phosgenite, 139.

Pigotite, 104.

Pinite, 100.

Pins, ironstone, 119.

Pipe veins, 132.

Pisolitic iron-ore, Antrim, 229.

North Wales, 126.

Pitchblende, 79.
Plaster stone, 183.
Plumbago, 159.
Plumbo-aragonite, 209.
Plumbo-calcite, 209.
Plumosite, 233.
Plush, copper-ore, 42.
Pneumatolysis, 11.
Poder, 44.
Polianite, 77.
Polonium, 80.
Polytelite, 233.
Potato-stones, 111.
Potters' ore, 137.

stone, 183.

Precipitate, copper, Anglesea, 127.

Wicklow, 224.

Prehnite, 101, 216.
Przibramite, §14,

240

TNDEX.

Pseudomalachite, 52.
Pseudomorphs, 13, 55, 69, 142, 146,

163.
Pseudophite, 102.
Psilomelane, 77.
Puddle-ore, 145.
Purple copper-ore, 39.
Pyrargyrite, 57.
Pyrites (pyrite), Cornwall, 60.

Forest-of Dean, 117.

S. Wales, 119.

in Neozoic strata, 196.

Pyrites, arsenical, 31.
hair, 120.

- — magnetic, 168.

nickel, 120.

■ rhombic, 198.

tin, 20.

Pyritohedron, 61.
Pyritoids, 62.
Pyroelectricity, 159.
Pyroemerald, 88.
Pyrolusite, 77.
Pyromorphite, Cornwall, 56.

Cumberland, 155.

Leadhills, 207.

Pyrophosphorescence, 88.
Pyrrhotite (pyrrhotine), 167.

Quartz, Cornwall, 21, 90.
Cumberland, 148, 176.

— Snowdon, 129.

in Neozoic strata, 199.

Quartz, milky, 129.

Radio-active minerals, 80.

Radio-tellurium, 80.

Radium, 80.

Rake veins, 131, 161.

Ra.shleigh collection, 62.

Ratholite, 218.

Red copper-ore, 42.

iron-ore, 144

Reddle, ill.
Redruthite, 37.
Re-entrant angles, 1").
Resin, Highgate, 203.
Restormel Royal Mine, 65.
Restormelite, 103.
Retinasphalt, 104.
Retinite, 104.
Rhodoehrosite, 77.
Rhodonite, 78, 120.
Ribband veinstones, 21.
Right-running veins, 161.
Rock-crystal, 91.
Rock-salt, 181, 230.
Roscoelite, 191.
Rose spar, 77.
Rosedale iron-ore, 192.
Rosin blende, 141.

tin, 16.

Round ore (galena), 123.
Ruby blende, 124.

Ruby copper-ore, 42.
Ruddle, 111, 144.
Rugg stones, 199.
Untile, 100, 128, 226.

Saline alteration of pyrites, 197.
Salt, Cheshire, 181.

Ireland, 230.

Sammetblende, 68.
Sanidine, 99.
Saponite, 103.
Satin-spar, 173, 183.
Saussurite, 103.
Scarbroite, 200.
Sceptre quartz, 225.
Schaumkalk, 173.
Scheelite 31, 153.
Schiefer spar, 93, 210.
Schillerisation, 103.
Schorl, 28.
Schorl-rock, 29.
Schroetterite, 103.
Scorodite, 73.
Scotch pebbles, 218.
Scotland, minerals of, 205.
Seals on crystals, 162
Secretion, lateral 14.
Selenite, 183
Serpentine, 102
Shining ore, 67.
Shropshire, minerals of 177
Siderite, 69.
Sidot's blende, 214.
Silver, native, 57.
Silver ores, Cornwall, 56.
Slate spar, 93, 210.
Slickensides, 138.
Slippers (pseudomorphs), 70.
Smaltite (smaltine) 76.
Smith ore, 116.
Smithsonite 158
Smoky quartz, 91, 148, 220.
Smoky topaz, 220.
Soap stone, 103.
Solfatara, 31

Somersetshire, minerals of, 105.
Soot, arsenical, 32
Spangolite ? 48.
Sparable tin, IS.
Sparry iron-ore, 106.
Spathic iron-ore, 106.
Spatum Islandicum, 124.
Specular iron-ore, 67, 147.
Sphierosiderite, 120.
Sphalerite, 58, 141.
Stalactites, 133, 202.
Stalactitic barytes, 136.
Stalagmites, 133, 202.
Stannite (stannine), 20, 23.
Steatite,_ 103.
Stephanite, 57.
Stibnite, 59.
Stilbite, 217, 221.
Stilpnosiderite, 195,

INltEX.

241

St.ikesite, 23.
Stream tin, 17.
Strontian, minerals of, 21 o.
Strontian spar, 211.
Stnmtianite, 211.
Strontium, 114, 211.
Sugar-candy spar, y.\ 202.
Sugary spar, 21.
Sulphur, native, 1«:>. 220.
Sulphur-' .re, 224.
Susannite, 2ns.

Tallingite, 49.
Tamarite, 53.
Tarnowitzite, 2D9.
Tavistoekite, 99.
Tennantite, 04.
Tenorite, 14.
Terra ponderosa, 170.
Tetradyniite, 1.54.
Tetrahedrite, 64.
Thomsonite, 210.
Thunderbolts, 19*.
Tile-ore, 42.
Tin, black, 8.

, native, 7.

, needle, 16.

, sparable, 10.

, white, 8.

Tin-ore, 15, 22' i, 223.
Tin pyrites, 20.
Tinstone, Cornwall 1").

Ross-shire, 22<>.

Wicklow, 223.

Titanium, 191.
Toad's-eye tin, 1 7.
Toad.-,tone, 131.
Tooth-tin, 16.
Topaz, Cornwall 25.

Ireland, 228.

Scotland, 220.

Torberite (Torbernite), c 3.
Tourmaline, 28.
Towanite, 35.
Travertine, 133.
Troilite, 141.
Trowlesworthite, 20.
Tungstic ochre, 153.
Tungstite, 31, 153.
Turf copper-mine, 127.
Turgite, 147.

("lster, minerals of, 227.
Unstable quartz, 92.
Uraninite, \\).
Uranite, 81.
Uranium mica, 82.

ochre, 81.

ores, 79.

Vadose region, 41.
Vanadinite, 207.
Variegated copper-ore, 39.
Varviscite, 179.
Veins, mineral, 6, 84.
Vesuvian, 227.
Virgin copper, 44.
Vitreous copper ore, 37.
Vivianite, 70.
Volborthite, 191.
Vugs, 6, 85.

Wad, 159.

Wales, minerals of, 117.
Waringtonite, 47.
Wavellite, Devon, 98.

Ireland, 232.

Waxen vein, 138.

Wealden iron-ore, 1 93.

Websterite, 201.

Welsh Gold, 129.

Western Isles, minerals ._>t, 221

Wheal, 13.

Wheat stone, 138.

White iron-ore, 106.

White lead-ore, 138.

Wicklow, copper, 224.

gold, 222.

Willemite, 158.
Withamite, 219.
Witherite, 170, 17k.
Wolfram, Cornwall, 30.

Cumberland, 153.

Wolframine, 31.
Wolframite, 30.
Wolfram ochre, 31.
Wonder stone, 202.
Wood arsenate, 51.

copper, 51.

— iron-ore, 68.
— — tin, 16.
Woodwardite, 47.
Wulfenite, 154.

Xanthosiderite, 195.
Yellow copper-ore, 35.

Zeolites, 215, 221.
Zinc-ores, Cornwall, 58.

Cumberland, 165.

— Derbyshire, 140.

Isle of Man, 233.

Leadhills, 209.

Mendips, 109.

Zinnwaldite, 27.
Zippeite, 81.
Z witter, 12.

7882.

SHEET MEMOLBS OF OLD SEEIES MAPS— continued.

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50 SW

50 NW .

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t; e

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sJ SE

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■y. -w

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THE MUSEUM OP PRACTICAL GEOLOGY,

Jermyn Street, S.W.,

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Full text of "A handbook to a collection of the minerals of the British Islands, mostly selected from the Ludlam collection, in the Museum of Practical Geology"

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